import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextLong();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextLong();
        }
        long ans = 0l;
        for (int i = 0; i < n; i++) {
            long l = Math.min(a[i], b[i]);
            a[i] -= l;
            b[i] -= l;
            ans += l;
            long r = Math.min(a[i+1], b[i]);
            a[i+1] -= r;
            b[i] -= r;
            ans += r;
        }
        System.out.println(ans);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextLong();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextLong();
        }
        long ans = 0l;
        for (int i = 0; i < n; i++) {
            long l = Math.min(a[i], b[i]);
            a[i] -= l;
            b[i] -= l;
            ans += l;
            long r = Math.min(a[i+1], b[i]);
            a[i+1] -= r;
            b[i] -= r;
            ans += r;
        }
        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextLong();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextLong();
        }
        long ans = 0l;
        for (int i = 0; i < n; i++) {
            long l = Math.min(a[i], b[i]);
            a[i] -= l;
            b[i] -= l;
            ans += l;
            long r = Math.min(a[i+1], b[i]);
            a[i+1] -= r;
            b[i] -= r;
            ans += r;
        }
        System.out.println(ans);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextLong();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextLong();
        }
        long ans = 0l;
        for (int i = 0; i < n; i++) {
            long l = Math.min(a[i], b[i]);
            a[i] -= l;
            b[i] -= l;
            ans += l;
            long r = Math.min(a[i+1], b[i]);
            a[i+1] -= r;
            b[i] -= r;
            ans += r;
        }
        System.out.println(ans);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc 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 + 1; i++) {
            a[i] = sc.nextLong();
        } int i = 0; int i = 0; i 0 i < n + 1 i n + 1 n 1 i++ i++ i {
            a[i] = sc.nextLong();
        } {
            a[i] = sc.nextLong();
        } a[i] = sc.nextLong() a[i] a i sc.nextLong() sc.nextLong sc for (int i = 0; i < n; i++) {
            b[i] = sc.nextLong();
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            b[i] = sc.nextLong();
        } {
            b[i] = sc.nextLong();
        } b[i] = sc.nextLong() b[i] b i sc.nextLong() sc.nextLong sc long ans = 0l; ans 0l for (int i = 0; i < n; i++) {
            long l = Math.min(a[i], b[i]);
            a[i] -= l;
            b[i] -= l;
            ans += l;
            long r = Math.min(a[i+1], b[i]);
            a[i+1] -= r;
            b[i] -= r;
            ans += r;
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            long l = Math.min(a[i], b[i]);
            a[i] -= l;
            b[i] -= l;
            ans += l;
            long r = Math.min(a[i+1], b[i]);
            a[i+1] -= r;
            b[i] -= r;
            ans += r;
        } {
            long l = Math.min(a[i], b[i]);
            a[i] -= l;
            b[i] -= l;
            ans += l;
            long r = Math.min(a[i+1], b[i]);
            a[i+1] -= r;
            b[i] -= r;
            ans += r;
        } long l = Math.min(a[i], b[i]); l Math.min(a[i], b[i]) Math.min Math a[i] a i b[i] b i a[i] -= l a[i] a i l b[i] -= l b[i] b i l ans += l ans l long r = Math.min(a[i+1], b[i]); r Math.min(a[i+1], b[i]) Math.min Math a[i+1] a i+1 i 1 b[i] b i a[i+1] -= r a[i+1] a i+1 i 1 r b[i] -= r b[i] b i r ans += r ans r System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextLong();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextLong();
        }
        long ans = 0l;
        for (int i = 0; i < n; i++) {
            long l = Math.min(a[i], b[i]);
            a[i] -= l;
            b[i] -= l;
            ans += l;
            long r = Math.min(a[i+1], b[i]);
            a[i+1] -= r;
            b[i] -= r;
            ans += r;
        }
        System.out.println(ans);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextLong();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextLong();
        }
        long ans = 0l;
        for (int i = 0; i < n; i++) {
            long l = Math.min(a[i], b[i]);
            a[i] -= l;
            b[i] -= l;
            ans += l;
            long r = Math.min(a[i+1], b[i]);
            a[i+1] -= r;
            b[i] -= r;
            ans += r;
        }
        System.out.println(ans);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextLong();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextLong();
        }
        long ans = 0l;
        for (int i = 0; i < n; i++) {
            long l = Math.min(a[i], b[i]);
            a[i] -= l;
            b[i] -= l;
            ans += l;
            long r = Math.min(a[i+1], b[i]);
            a[i+1] -= r;
            b[i] -= r;
            ans += r;
        }
        System.out.println(ans);
    }
}