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

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskC solver = new TaskC();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskC {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            int n = in.nextInt();
            long[] a = new long[n + 1];
            long[] b = new long[n];
            for (int i = 0; i <= n; i++)
                a[i] = in.nextInt();
            for (int i = 0; i < n; i++)
                b[i] = in.nextInt();
            long ans, rest;
            if (b[0] >= a[0]) {
                ans = a[0];
                rest = b[0] - a[0];
            } else {
                ans = b[0];
                rest = 0;
            }
            for (int i = 1; i < n; i++) {
                long can = rest + b[i];
                if (can >= a[i]) {
                    ans += a[i];
                    rest = Math.min(can - a[i], b[i]);
                } else {
                    ans += can;
                    rest = 0;
                }
            }
            if (rest > 0) {
                if (rest >= a[n])
                    ans += a[n];
                else
                    ans += rest;
            }
            out.println(ans);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

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

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

    }
} import java.io.OutputStream; OutputStream java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.StringTokenizer; StringTokenizer java.util import java.io.IOException; IOException java.io import java.io.BufferedReader; BufferedReader java.io import java.io.InputStreamReader; InputStreamReader java.io import java.io.InputStream; InputStream java.io public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskC solver = new TaskC();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskC {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            int n = in.nextInt();
            long[] a = new long[n + 1];
            long[] b = new long[n];
            for (int i = 0; i <= n; i++)
                a[i] = in.nextInt();
            for (int i = 0; i < n; i++)
                b[i] = in.nextInt();
            long ans, rest;
            if (b[0] >= a[0]) {
                ans = a[0];
                rest = b[0] - a[0];
            } else {
                ans = b[0];
                rest = 0;
            }
            for (int i = 1; i < n; i++) {
                long can = rest + b[i];
                if (can >= a[i]) {
                    ans += a[i];
                    rest = Math.min(can - a[i], b[i]);
                } else {
                    ans += can;
                    rest = 0;
                }
            }
            if (rest > 0) {
                if (rest >= a[n])
                    ans += a[n];
                else
                    ans += rest;
            }
            out.println(ans);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

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

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

    }
} Main public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskC solver = new TaskC();
        solver.solve(1, in, out);
        out.close();
    } main {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskC solver = new TaskC();
        solver.solve(1, in, out);
        out.close();
    } InputStream inputStream = System.in; inputStream System.in System System.in OutputStream outputStream = System.out; outputStream System.out System System.out InputReader in = new InputReader(inputStream); in new InputReader(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) TaskC solver = new TaskC(); solver new TaskC() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class TaskC {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            int n = in.nextInt();
            long[] a = new long[n + 1];
            long[] b = new long[n];
            for (int i = 0; i <= n; i++)
                a[i] = in.nextInt();
            for (int i = 0; i < n; i++)
                b[i] = in.nextInt();
            long ans, rest;
            if (b[0] >= a[0]) {
                ans = a[0];
                rest = b[0] - a[0];
            } else {
                ans = b[0];
                rest = 0;
            }
            for (int i = 1; i < n; i++) {
                long can = rest + b[i];
                if (can >= a[i]) {
                    ans += a[i];
                    rest = Math.min(can - a[i], b[i]);
                } else {
                    ans += can;
                    rest = 0;
                }
            }
            if (rest > 0) {
                if (rest >= a[n])
                    ans += a[n];
                else
                    ans += rest;
            }
            out.println(ans);
        }

    } TaskC public void solve(int testNumber, InputReader in, PrintWriter out) {
            int n = in.nextInt();
            long[] a = new long[n + 1];
            long[] b = new long[n];
            for (int i = 0; i <= n; i++)
                a[i] = in.nextInt();
            for (int i = 0; i < n; i++)
                b[i] = in.nextInt();
            long ans, rest;
            if (b[0] >= a[0]) {
                ans = a[0];
                rest = b[0] - a[0];
            } else {
                ans = b[0];
                rest = 0;
            }
            for (int i = 1; i < n; i++) {
                long can = rest + b[i];
                if (can >= a[i]) {
                    ans += a[i];
                    rest = Math.min(can - a[i], b[i]);
                } else {
                    ans += can;
                    rest = 0;
                }
            }
            if (rest > 0) {
                if (rest >= a[n])
                    ans += a[n];
                else
                    ans += rest;
            }
            out.println(ans);
        } solve {
            int n = in.nextInt();
            long[] a = new long[n + 1];
            long[] b = new long[n];
            for (int i = 0; i <= n; i++)
                a[i] = in.nextInt();
            for (int i = 0; i < n; i++)
                b[i] = in.nextInt();
            long ans, rest;
            if (b[0] >= a[0]) {
                ans = a[0];
                rest = b[0] - a[0];
            } else {
                ans = b[0];
                rest = 0;
            }
            for (int i = 1; i < n; i++) {
                long can = rest + b[i];
                if (can >= a[i]) {
                    ans += a[i];
                    rest = Math.min(can - a[i], b[i]);
                } else {
                    ans += can;
                    rest = 0;
                }
            }
            if (rest > 0) {
                if (rest >= a[n])
                    ans += a[n];
                else
                    ans += rest;
            }
            out.println(ans);
        } int n = in.nextInt(); n in.nextInt() in.nextInt in long[] a = new long[n + 1]; a new long[n + 1] n + 1 n 1 long[] b = new long[n]; b new long[n] n for (int i = 0; i <= n; i++)
                a[i] = in.nextInt(); int i = 0; int i = 0; i 0 i <= n i n i++ i++ i a[i] = in.nextInt(); a[i] = in.nextInt() a[i] a i in.nextInt() in.nextInt in for (int i = 0; i < n; i++)
                b[i] = in.nextInt(); int i = 0; int i = 0; i 0 i < n i n i++ i++ i b[i] = in.nextInt(); b[i] = in.nextInt() b[i] b i in.nextInt() in.nextInt in long ans ans rest; rest if (b[0] >= a[0]) {
                ans = a[0];
                rest = b[0] - a[0];
            } else {
                ans = b[0];
                rest = 0;
            } b[0] >= a[0] b[0] b 0 a[0] a 0 {
                ans = a[0];
                rest = b[0] - a[0];
            } ans = a[0] ans a[0] a 0 rest = b[0] - a[0] rest b[0] - a[0] b[0] b 0 a[0] a 0 {
                ans = b[0];
                rest = 0;
            } ans = b[0] ans b[0] b 0 rest = 0 rest 0 for (int i = 1; i < n; i++) {
                long can = rest + b[i];
                if (can >= a[i]) {
                    ans += a[i];
                    rest = Math.min(can - a[i], b[i]);
                } else {
                    ans += can;
                    rest = 0;
                }
            } int i = 1; int i = 1; i 1 i < n i n i++ i++ i {
                long can = rest + b[i];
                if (can >= a[i]) {
                    ans += a[i];
                    rest = Math.min(can - a[i], b[i]);
                } else {
                    ans += can;
                    rest = 0;
                }
            } {
                long can = rest + b[i];
                if (can >= a[i]) {
                    ans += a[i];
                    rest = Math.min(can - a[i], b[i]);
                } else {
                    ans += can;
                    rest = 0;
                }
            } long can = rest + b[i]; can rest + b[i] rest b[i] b i if (can >= a[i]) {
                    ans += a[i];
                    rest = Math.min(can - a[i], b[i]);
                } else {
                    ans += can;
                    rest = 0;
                } can >= a[i] can a[i] a i {
                    ans += a[i];
                    rest = Math.min(can - a[i], b[i]);
                } ans += a[i] ans a[i] a i rest = Math.min(can - a[i], b[i]) rest Math.min(can - a[i], b[i]) Math.min Math can - a[i] can a[i] a i b[i] b i {
                    ans += can;
                    rest = 0;
                } ans += can ans can rest = 0 rest 0 if (rest > 0) {
                if (rest >= a[n])
                    ans += a[n];
                else
                    ans += rest;
            } rest > 0 rest 0 {
                if (rest >= a[n])
                    ans += a[n];
                else
                    ans += rest;
            } if (rest >= a[n])
                    ans += a[n];
                else
                    ans += rest; rest >= a[n] rest a[n] a n ans += a[n] ans a[n] a n ans += rest ans rest out.println(ans) out.println out ans int testNumber testNumber InputReader in in PrintWriter out out static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

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

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

    } InputReader public BufferedReader reader; reader public StringTokenizer tokenizer; tokenizer public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        } InputReader {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        } reader = new BufferedReader(new InputStreamReader(stream), 32768) reader new BufferedReader(new InputStreamReader(stream), 32768) tokenizer = null tokenizer null InputStream stream stream public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        } next {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        } while (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 int nextInt() {
            return Integer.parseInt(next());
        } nextInt {
            return Integer.parseInt(next());
        } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskC solver = new TaskC();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskC {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            int n = in.nextInt();
            long[] a = new long[n + 1];
            long[] b = new long[n];
            for (int i = 0; i <= n; i++)
                a[i] = in.nextInt();
            for (int i = 0; i < n; i++)
                b[i] = in.nextInt();
            long ans, rest;
            if (b[0] >= a[0]) {
                ans = a[0];
                rest = b[0] - a[0];
            } else {
                ans = b[0];
                rest = 0;
            }
            for (int i = 1; i < n; i++) {
                long can = rest + b[i];
                if (can >= a[i]) {
                    ans += a[i];
                    rest = Math.min(can - a[i], b[i]);
                } else {
                    ans += can;
                    rest = 0;
                }
            }
            if (rest > 0) {
                if (rest >= a[n])
                    ans += a[n];
                else
                    ans += rest;
            }
            out.println(ans);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

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

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

    }
} public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskC solver = new TaskC();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskC {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            int n = in.nextInt();
            long[] a = new long[n + 1];
            long[] b = new long[n];
            for (int i = 0; i <= n; i++)
                a[i] = in.nextInt();
            for (int i = 0; i < n; i++)
                b[i] = in.nextInt();
            long ans, rest;
            if (b[0] >= a[0]) {
                ans = a[0];
                rest = b[0] - a[0];
            } else {
                ans = b[0];
                rest = 0;
            }
            for (int i = 1; i < n; i++) {
                long can = rest + b[i];
                if (can >= a[i]) {
                    ans += a[i];
                    rest = Math.min(can - a[i], b[i]);
                } else {
                    ans += can;
                    rest = 0;
                }
            }
            if (rest > 0) {
                if (rest >= a[n])
                    ans += a[n];
                else
                    ans += rest;
            }
            out.println(ans);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

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

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

    }
} Main
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.StringTokenizer;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskC solver = new TaskC();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskC {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            int n = in.nextInt();
            long[] a = new long[n + 1];
            long[] b = new long[n];
            for (int i = 0; i <= n; i++)
                a[i] = in.nextInt();
            for (int i = 0; i < n; i++)
                b[i] = in.nextInt();
            long ans, rest;
            if (b[0] >= a[0]) {
                ans = a[0];
                rest = b[0] - a[0];
            } else {
                ans = b[0];
                rest = 0;
            }
            for (int i = 1; i < n; i++) {
                long can = rest + b[i];
                if (can >= a[i]) {
                    ans += a[i];
                    rest = Math.min(can - a[i], b[i]);
                } else {
                    ans += can;
                    rest = 0;
                }
            }
            if (rest > 0) {
                if (rest >= a[n])
                    ans += a[n];
                else
                    ans += rest;
            }
            out.println(ans);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

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

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

    }
}