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 sc = new FastScanner(System.in);

		int n = sc.nextInt();
		int[] a = sc.nextIntArray(n + 1);
		int[] b = sc.nextIntArray(n);

		long res = 0;

		for (int i = 0; i < n; i++) {
			if (a[i] - b[i] >= 0) {
				res += b[i];
				b[i] = 0;
				a[i] -= b[i];
			} else {
				res += a[i];
				b[i] -= a[i];
				a[i] = 0;
			}

			if (b[i] != 0) {
				if (a[i + 1] - b[i] >= 0) {
					res += b[i];
					a[i + 1] -= b[i];
				} else {
					res += a[i + 1];
					a[i + 1] = 0;
				}
			}
		}

		System.out.println(res);
	}

	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 sc = new FastScanner(System.in);

		int n = sc.nextInt();
		int[] a = sc.nextIntArray(n + 1);
		int[] b = sc.nextIntArray(n);

		long res = 0;

		for (int i = 0; i < n; i++) {
			if (a[i] - b[i] >= 0) {
				res += b[i];
				b[i] = 0;
				a[i] -= b[i];
			} else {
				res += a[i];
				b[i] -= a[i];
				a[i] = 0;
			}

			if (b[i] != 0) {
				if (a[i + 1] - b[i] >= 0) {
					res += b[i];
					a[i + 1] -= b[i];
				} else {
					res += a[i + 1];
					a[i + 1] = 0;
				}
			}
		}

		System.out.println(res);
	}

	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 sc = new FastScanner(System.in);

		int n = sc.nextInt();
		int[] a = sc.nextIntArray(n + 1);
		int[] b = sc.nextIntArray(n);

		long res = 0;

		for (int i = 0; i < n; i++) {
			if (a[i] - b[i] >= 0) {
				res += b[i];
				b[i] = 0;
				a[i] -= b[i];
			} else {
				res += a[i];
				b[i] -= a[i];
				a[i] = 0;
			}

			if (b[i] != 0) {
				if (a[i + 1] - b[i] >= 0) {
					res += b[i];
					a[i + 1] -= b[i];
				} else {
					res += a[i + 1];
					a[i + 1] = 0;
				}
			}
		}

		System.out.println(res);
	} main {
		FastScanner sc = new FastScanner(System.in);

		int n = sc.nextInt();
		int[] a = sc.nextIntArray(n + 1);
		int[] b = sc.nextIntArray(n);

		long res = 0;

		for (int i = 0; i < n; i++) {
			if (a[i] - b[i] >= 0) {
				res += b[i];
				b[i] = 0;
				a[i] -= b[i];
			} else {
				res += a[i];
				b[i] -= a[i];
				a[i] = 0;
			}

			if (b[i] != 0) {
				if (a[i + 1] - b[i] >= 0) {
					res += b[i];
					a[i + 1] -= b[i];
				} else {
					res += a[i + 1];
					a[i + 1] = 0;
				}
			}
		}

		System.out.println(res);
	} FastScanner sc = new FastScanner(System.in); sc new FastScanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] a = sc.nextIntArray(n + 1); a sc.nextIntArray(n + 1) sc.nextIntArray sc n + 1 n 1 int[] b = sc.nextIntArray(n); b sc.nextIntArray(n) sc.nextIntArray sc n long res = 0; res 0 for (int i = 0; i < n; i++) {
			if (a[i] - b[i] >= 0) {
				res += b[i];
				b[i] = 0;
				a[i] -= b[i];
			} else {
				res += a[i];
				b[i] -= a[i];
				a[i] = 0;
			}

			if (b[i] != 0) {
				if (a[i + 1] - b[i] >= 0) {
					res += b[i];
					a[i + 1] -= b[i];
				} else {
					res += a[i + 1];
					a[i + 1] = 0;
				}
			}
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			if (a[i] - b[i] >= 0) {
				res += b[i];
				b[i] = 0;
				a[i] -= b[i];
			} else {
				res += a[i];
				b[i] -= a[i];
				a[i] = 0;
			}

			if (b[i] != 0) {
				if (a[i + 1] - b[i] >= 0) {
					res += b[i];
					a[i + 1] -= b[i];
				} else {
					res += a[i + 1];
					a[i + 1] = 0;
				}
			}
		} {
			if (a[i] - b[i] >= 0) {
				res += b[i];
				b[i] = 0;
				a[i] -= b[i];
			} else {
				res += a[i];
				b[i] -= a[i];
				a[i] = 0;
			}

			if (b[i] != 0) {
				if (a[i + 1] - b[i] >= 0) {
					res += b[i];
					a[i + 1] -= b[i];
				} else {
					res += a[i + 1];
					a[i + 1] = 0;
				}
			}
		} if (a[i] - b[i] >= 0) {
				res += b[i];
				b[i] = 0;
				a[i] -= b[i];
			} else {
				res += a[i];
				b[i] -= a[i];
				a[i] = 0;
			} a[i] - b[i] >= 0 a[i] - b[i] a[i] a i b[i] b i 0 {
				res += b[i];
				b[i] = 0;
				a[i] -= b[i];
			} res += b[i] res b[i] b i b[i] = 0 b[i] b i 0 a[i] -= b[i] a[i] a i b[i] b i {
				res += a[i];
				b[i] -= a[i];
				a[i] = 0;
			} res += a[i] res a[i] a i b[i] -= a[i] b[i] b i a[i] a i a[i] = 0 a[i] a i 0 if (b[i] != 0) {
				if (a[i + 1] - b[i] >= 0) {
					res += b[i];
					a[i + 1] -= b[i];
				} else {
					res += a[i + 1];
					a[i + 1] = 0;
				}
			} b[i] != 0 b[i] b i 0 {
				if (a[i + 1] - b[i] >= 0) {
					res += b[i];
					a[i + 1] -= b[i];
				} else {
					res += a[i + 1];
					a[i + 1] = 0;
				}
			} if (a[i + 1] - b[i] >= 0) {
					res += b[i];
					a[i + 1] -= b[i];
				} else {
					res += a[i + 1];
					a[i + 1] = 0;
				} a[i + 1] - b[i] >= 0 a[i + 1] - b[i] a[i + 1] a i + 1 i 1 b[i] b i 0 {
					res += b[i];
					a[i + 1] -= b[i];
				} res += b[i] res b[i] b i a[i + 1] -= b[i] a[i + 1] a i + 1 i 1 b[i] b i {
					res += a[i + 1];
					a[i + 1] = 0;
				} res += a[i + 1] res a[i + 1] a i + 1 i 1 a[i + 1] = 0 a[i + 1] a i + 1 i 1 0 System.out.println(res) System.out.println System.out System System.out res 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 sc = new FastScanner(System.in);

		int n = sc.nextInt();
		int[] a = sc.nextIntArray(n + 1);
		int[] b = sc.nextIntArray(n);

		long res = 0;

		for (int i = 0; i < n; i++) {
			if (a[i] - b[i] >= 0) {
				res += b[i];
				b[i] = 0;
				a[i] -= b[i];
			} else {
				res += a[i];
				b[i] -= a[i];
				a[i] = 0;
			}

			if (b[i] != 0) {
				if (a[i + 1] - b[i] >= 0) {
					res += b[i];
					a[i + 1] -= b[i];
				} else {
					res += a[i + 1];
					a[i + 1] = 0;
				}
			}
		}

		System.out.println(res);
	}

	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 sc = new FastScanner(System.in);

		int n = sc.nextInt();
		int[] a = sc.nextIntArray(n + 1);
		int[] b = sc.nextIntArray(n);

		long res = 0;

		for (int i = 0; i < n; i++) {
			if (a[i] - b[i] >= 0) {
				res += b[i];
				b[i] = 0;
				a[i] -= b[i];
			} else {
				res += a[i];
				b[i] -= a[i];
				a[i] = 0;
			}

			if (b[i] != 0) {
				if (a[i + 1] - b[i] >= 0) {
					res += b[i];
					a[i + 1] -= b[i];
				} else {
					res += a[i + 1];
					a[i + 1] = 0;
				}
			}
		}

		System.out.println(res);
	}

	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 sc = new FastScanner(System.in);

		int n = sc.nextInt();
		int[] a = sc.nextIntArray(n + 1);
		int[] b = sc.nextIntArray(n);

		long res = 0;

		for (int i = 0; i < n; i++) {
			if (a[i] - b[i] >= 0) {
				res += b[i];
				b[i] = 0;
				a[i] -= b[i];
			} else {
				res += a[i];
				b[i] -= a[i];
				a[i] = 0;
			}

			if (b[i] != 0) {
				if (a[i + 1] - b[i] >= 0) {
					res += b[i];
					a[i + 1] -= b[i];
				} else {
					res += a[i + 1];
					a[i + 1] = 0;
				}
			}
		}

		System.out.println(res);
	}

	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;
		}

	}
}