import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {

    public static void main(String[] args) {
        FastScanner scan = new FastScanner(System.in);
        final int N = scan.nextInt();
        long[] A = new long[N + 1];
        for (int i = 0; i < N + 1; i++) {
            A[i] = scan.nextLong();
        }
        long[] B = new long[N];
        for (int i = 0; i < N; i++) {
            B[i] = scan.nextLong();
        }

        long totalBeated = 0;
        for (int i = 0; i < N; i++) {
            long beated = Long.min(A[i], B[i]);
            totalBeated += beated;
            B[i] -= beated;
            beated = Long.min(A[i + 1], B[i]);
            totalBeated += beated;
            A[i + 1] -= beated;
        }
        System.out.println(totalBeated);
    }

    static class FastScanner {
        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        public String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public double nextDouble() {
             return Double.parseDouble(next());
         }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        } 
    }
} import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.InputStreamReader; InputStreamReader java.io import java.util.StringTokenizer; StringTokenizer java.util public class Main {

    public static void main(String[] args) {
        FastScanner scan = new FastScanner(System.in);
        final int N = scan.nextInt();
        long[] A = new long[N + 1];
        for (int i = 0; i < N + 1; i++) {
            A[i] = scan.nextLong();
        }
        long[] B = new long[N];
        for (int i = 0; i < N; i++) {
            B[i] = scan.nextLong();
        }

        long totalBeated = 0;
        for (int i = 0; i < N; i++) {
            long beated = Long.min(A[i], B[i]);
            totalBeated += beated;
            B[i] -= beated;
            beated = Long.min(A[i + 1], B[i]);
            totalBeated += beated;
            A[i + 1] -= beated;
        }
        System.out.println(totalBeated);
    }

    static class FastScanner {
        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        public String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public double nextDouble() {
             return Double.parseDouble(next());
         }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        } 
    }
} Main public static void main(String[] args) {
        FastScanner scan = new FastScanner(System.in);
        final int N = scan.nextInt();
        long[] A = new long[N + 1];
        for (int i = 0; i < N + 1; i++) {
            A[i] = scan.nextLong();
        }
        long[] B = new long[N];
        for (int i = 0; i < N; i++) {
            B[i] = scan.nextLong();
        }

        long totalBeated = 0;
        for (int i = 0; i < N; i++) {
            long beated = Long.min(A[i], B[i]);
            totalBeated += beated;
            B[i] -= beated;
            beated = Long.min(A[i + 1], B[i]);
            totalBeated += beated;
            A[i + 1] -= beated;
        }
        System.out.println(totalBeated);
    } main {
        FastScanner scan = new FastScanner(System.in);
        final int N = scan.nextInt();
        long[] A = new long[N + 1];
        for (int i = 0; i < N + 1; i++) {
            A[i] = scan.nextLong();
        }
        long[] B = new long[N];
        for (int i = 0; i < N; i++) {
            B[i] = scan.nextLong();
        }

        long totalBeated = 0;
        for (int i = 0; i < N; i++) {
            long beated = Long.min(A[i], B[i]);
            totalBeated += beated;
            B[i] -= beated;
            beated = Long.min(A[i + 1], B[i]);
            totalBeated += beated;
            A[i + 1] -= beated;
        }
        System.out.println(totalBeated);
    } FastScanner scan = new FastScanner(System.in); scan new FastScanner(System.in) final int N = scan.nextInt(); N scan.nextInt() scan.nextInt scan long[] A = new long[N + 1]; A new long[N + 1] N + 1 N 1 for (int i = 0; i < N + 1; i++) {
            A[i] = scan.nextLong();
        } int i = 0; int i = 0; i 0 i < N + 1 i N + 1 N 1 i++ i++ i {
            A[i] = scan.nextLong();
        } {
            A[i] = scan.nextLong();
        } A[i] = scan.nextLong() A[i] A i scan.nextLong() scan.nextLong scan long[] B = new long[N]; B new long[N] N for (int i = 0; i < N; i++) {
            B[i] = scan.nextLong();
        } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
            B[i] = scan.nextLong();
        } {
            B[i] = scan.nextLong();
        } B[i] = scan.nextLong() B[i] B i scan.nextLong() scan.nextLong scan long totalBeated = 0; totalBeated 0 for (int i = 0; i < N; i++) {
            long beated = Long.min(A[i], B[i]);
            totalBeated += beated;
            B[i] -= beated;
            beated = Long.min(A[i + 1], B[i]);
            totalBeated += beated;
            A[i + 1] -= beated;
        } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
            long beated = Long.min(A[i], B[i]);
            totalBeated += beated;
            B[i] -= beated;
            beated = Long.min(A[i + 1], B[i]);
            totalBeated += beated;
            A[i + 1] -= beated;
        } {
            long beated = Long.min(A[i], B[i]);
            totalBeated += beated;
            B[i] -= beated;
            beated = Long.min(A[i + 1], B[i]);
            totalBeated += beated;
            A[i + 1] -= beated;
        } long beated = Long.min(A[i], B[i]); beated Long.min(A[i], B[i]) Long.min Long A[i] A i B[i] B i totalBeated += beated totalBeated beated B[i] -= beated B[i] B i beated beated = Long.min(A[i + 1], B[i]) beated Long.min(A[i + 1], B[i]) Long.min Long A[i + 1] A i + 1 i 1 B[i] B i totalBeated += beated totalBeated beated A[i + 1] -= beated A[i + 1] A i + 1 i 1 beated System.out.println(totalBeated) System.out.println System.out System System.out totalBeated String[] args args static class FastScanner {
        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        public String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public double nextDouble() {
             return Double.parseDouble(next());
         }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        } 
    } FastScanner private BufferedReader reader = null; reader null private StringTokenizer tokenizer = null; tokenizer null public FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        } FastScanner {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        } reader = new BufferedReader(new InputStreamReader(in)) reader new BufferedReader(new InputStreamReader(in)) tokenizer = null tokenizer null InputStream in in public String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        } next {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        } if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } tokenizer == null || !tokenizer.hasMoreTokens() tokenizer == null tokenizer null !tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } IOException e {
                    throw new RuntimeException(e);
                } throw new RuntimeException(e); new RuntimeException(e) {
                    tokenizer = new StringTokenizer(reader.readLine());
                } tokenizer = new StringTokenizer(reader.readLine()) tokenizer new StringTokenizer(reader.readLine()) return tokenizer.nextToken(); tokenizer.nextToken() tokenizer.nextToken tokenizer public String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        } nextLine {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        } if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } tokenizer == null || !tokenizer.hasMoreTokens() tokenizer == null tokenizer null !tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } IOException e {
                    throw new RuntimeException(e);
                } throw new RuntimeException(e); new RuntimeException(e) {
                    return reader.readLine();
                } return reader.readLine(); reader.readLine() reader.readLine reader return tokenizer.nextToken("\n"); tokenizer.nextToken("\n") tokenizer.nextToken tokenizer "\n" public long nextLong() {
            return Long.parseLong(next());
        } nextLong {
            return Long.parseLong(next());
        } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next public int nextInt() {
            return Integer.parseInt(next());
        } nextInt {
            return Integer.parseInt(next());
        } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next public double nextDouble() {
             return Double.parseDouble(next());
         } nextDouble {
             return Double.parseDouble(next());
         } return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        } nextIntArray {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        } int[] a = new int[n]; a new int[n] n for (int i = 0; i < n; i++)
                a[i] = nextInt(); int i = 0; int i = 0; i 0 i < n i n i++ i++ i a[i] = nextInt(); a[i] = nextInt() a[i] a i nextInt() nextInt return a; a int n n public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        } nextLongArray {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        } long[] a = new long[n]; a new long[n] n for (int i = 0; i < n; i++)
                a[i] = nextLong(); int i = 0; int i = 0; i 0 i < n i n i++ i++ i a[i] = nextLong(); a[i] = nextLong() a[i] a i nextLong() nextLong return a; a int n n public class Main {

    public static void main(String[] args) {
        FastScanner scan = new FastScanner(System.in);
        final int N = scan.nextInt();
        long[] A = new long[N + 1];
        for (int i = 0; i < N + 1; i++) {
            A[i] = scan.nextLong();
        }
        long[] B = new long[N];
        for (int i = 0; i < N; i++) {
            B[i] = scan.nextLong();
        }

        long totalBeated = 0;
        for (int i = 0; i < N; i++) {
            long beated = Long.min(A[i], B[i]);
            totalBeated += beated;
            B[i] -= beated;
            beated = Long.min(A[i + 1], B[i]);
            totalBeated += beated;
            A[i + 1] -= beated;
        }
        System.out.println(totalBeated);
    }

    static class FastScanner {
        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        public String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public double nextDouble() {
             return Double.parseDouble(next());
         }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        } 
    }
} public class Main {

    public static void main(String[] args) {
        FastScanner scan = new FastScanner(System.in);
        final int N = scan.nextInt();
        long[] A = new long[N + 1];
        for (int i = 0; i < N + 1; i++) {
            A[i] = scan.nextLong();
        }
        long[] B = new long[N];
        for (int i = 0; i < N; i++) {
            B[i] = scan.nextLong();
        }

        long totalBeated = 0;
        for (int i = 0; i < N; i++) {
            long beated = Long.min(A[i], B[i]);
            totalBeated += beated;
            B[i] -= beated;
            beated = Long.min(A[i + 1], B[i]);
            totalBeated += beated;
            A[i + 1] -= beated;
        }
        System.out.println(totalBeated);
    }

    static class FastScanner {
        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        public String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public double nextDouble() {
             return Double.parseDouble(next());
         }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        } 
    }
} Main
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {

    public static void main(String[] args) {
        FastScanner scan = new FastScanner(System.in);
        final int N = scan.nextInt();
        long[] A = new long[N + 1];
        for (int i = 0; i < N + 1; i++) {
            A[i] = scan.nextLong();
        }
        long[] B = new long[N];
        for (int i = 0; i < N; i++) {
            B[i] = scan.nextLong();
        }

        long totalBeated = 0;
        for (int i = 0; i < N; i++) {
            long beated = Long.min(A[i], B[i]);
            totalBeated += beated;
            B[i] -= beated;
            beated = Long.min(A[i + 1], B[i]);
            totalBeated += beated;
            A[i + 1] -= beated;
        }
        System.out.println(totalBeated);
    }

    static class FastScanner {
        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        public String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public double nextDouble() {
             return Double.parseDouble(next());
         }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        } 
    }
}