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; i++) {
			a[i] = sc.nextLong();
		}
		for(int i = 0; i < n; i++) {
			b[i] = sc.nextLong();
		}
		sc.close();
		long ans = 0;
		for(int i = 0; i < n; i++) {
			ans += Math.min(a[i], b[i]);
			ans += Math.min(a[i+1],Math.max(0, b[i]-a[i]));
			a[i+1] -= Math.min(a[i+1], Math.max(0, b[i]-a[i]));
		}
		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; i++) {
			a[i] = sc.nextLong();
		}
		for(int i = 0; i < n; i++) {
			b[i] = sc.nextLong();
		}
		sc.close();
		long ans = 0;
		for(int i = 0; i < n; i++) {
			ans += Math.min(a[i], b[i]);
			ans += Math.min(a[i+1],Math.max(0, b[i]-a[i]));
			a[i+1] -= Math.min(a[i+1], Math.max(0, b[i]-a[i]));
		}
		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; i++) {
			a[i] = sc.nextLong();
		}
		for(int i = 0; i < n; i++) {
			b[i] = sc.nextLong();
		}
		sc.close();
		long ans = 0;
		for(int i = 0; i < n; i++) {
			ans += Math.min(a[i], b[i]);
			ans += Math.min(a[i+1],Math.max(0, b[i]-a[i]));
			a[i+1] -= Math.min(a[i+1], Math.max(0, b[i]-a[i]));
		}
		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; i++) {
			a[i] = sc.nextLong();
		}
		for(int i = 0; i < n; i++) {
			b[i] = sc.nextLong();
		}
		sc.close();
		long ans = 0;
		for(int i = 0; i < n; i++) {
			ans += Math.min(a[i], b[i]);
			ans += Math.min(a[i+1],Math.max(0, b[i]-a[i]));
			a[i+1] -= Math.min(a[i+1], Math.max(0, b[i]-a[i]));
		}
		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; i++) {
			a[i] = sc.nextLong();
		} int i = 0; int i = 0; i 0 i <= n i n 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 sc.close() sc.close sc long ans = 0; ans 0 for(int i = 0; i < n; i++) {
			ans += Math.min(a[i], b[i]);
			ans += Math.min(a[i+1],Math.max(0, b[i]-a[i]));
			a[i+1] -= Math.min(a[i+1], Math.max(0, b[i]-a[i]));
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			ans += Math.min(a[i], b[i]);
			ans += Math.min(a[i+1],Math.max(0, b[i]-a[i]));
			a[i+1] -= Math.min(a[i+1], Math.max(0, b[i]-a[i]));
		} {
			ans += Math.min(a[i], b[i]);
			ans += Math.min(a[i+1],Math.max(0, b[i]-a[i]));
			a[i+1] -= Math.min(a[i+1], Math.max(0, b[i]-a[i]));
		} ans += Math.min(a[i], b[i]) ans Math.min(a[i], b[i]) Math.min Math a[i] a i b[i] b i ans += Math.min(a[i+1],Math.max(0, b[i]-a[i])) ans Math.min(a[i+1],Math.max(0, b[i]-a[i])) Math.min Math a[i+1] a i+1 i 1 Math.max(0, b[i]-a[i]) Math.max Math 0 b[i]-a[i] b[i] b i a[i] a i a[i+1] -= Math.min(a[i+1], Math.max(0, b[i]-a[i])) a[i+1] a i+1 i 1 Math.min(a[i+1], Math.max(0, b[i]-a[i])) Math.min Math a[i+1] a i+1 i 1 Math.max(0, b[i]-a[i]) Math.max Math 0 b[i]-a[i] b[i] b i a[i] a i 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; i++) {
			a[i] = sc.nextLong();
		}
		for(int i = 0; i < n; i++) {
			b[i] = sc.nextLong();
		}
		sc.close();
		long ans = 0;
		for(int i = 0; i < n; i++) {
			ans += Math.min(a[i], b[i]);
			ans += Math.min(a[i+1],Math.max(0, b[i]-a[i]));
			a[i+1] -= Math.min(a[i+1], Math.max(0, b[i]-a[i]));
		}
		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; i++) {
			a[i] = sc.nextLong();
		}
		for(int i = 0; i < n; i++) {
			b[i] = sc.nextLong();
		}
		sc.close();
		long ans = 0;
		for(int i = 0; i < n; i++) {
			ans += Math.min(a[i], b[i]);
			ans += Math.min(a[i+1],Math.max(0, b[i]-a[i]));
			a[i+1] -= Math.min(a[i+1], Math.max(0, b[i]-a[i]));
		}
		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; i++) {
			a[i] = sc.nextLong();
		}
		for(int i = 0; i < n; i++) {
			b[i] = sc.nextLong();
		}
		sc.close();
		long ans = 0;
		for(int i = 0; i < n; i++) {
			ans += Math.min(a[i], b[i]);
			ans += Math.min(a[i+1],Math.max(0, b[i]-a[i]));
			a[i+1] -= Math.min(a[i+1], Math.max(0, b[i]-a[i]));
		}
		System.out.println(ans);
	}
}