import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n + 1];
		int[] b = new int[n];
		for (int i = 0; i < n + 1; i++) {
			a[i] = sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			b[i] = sc.nextInt();
		}
		sc.close();

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

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

		long ans = 0;
		for (int i = n - 1; i >= 0; i--) {
			long val = Math.min(a[i + 1], b[i]);
			ans += val;
			b[i] -= val;
			val = Math.min(a[i], b[i]);
			ans += val;
			a[i] -= val;
		}
		System.out.println(ans);
	} main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n + 1];
		int[] b = new int[n];
		for (int i = 0; i < n + 1; i++) {
			a[i] = sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			b[i] = sc.nextInt();
		}
		sc.close();

		long ans = 0;
		for (int i = n - 1; i >= 0; i--) {
			long val = Math.min(a[i + 1], b[i]);
			ans += val;
			b[i] -= val;
			val = Math.min(a[i], b[i]);
			ans += val;
			a[i] -= val;
		}
		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 int[] a = new int[n + 1]; a new int[n + 1] n + 1 n 1 int[] b = new int[n]; b new int[n] n for (int i = 0; i < n + 1; i++) {
			a[i] = sc.nextInt();
		} int i = 0; int i = 0; i 0 i < n + 1 i n + 1 n 1 i++ i++ i {
			a[i] = sc.nextInt();
		} {
			a[i] = sc.nextInt();
		} a[i] = sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc for (int i = 0; i < n; i++) {
			b[i] = sc.nextInt();
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			b[i] = sc.nextInt();
		} {
			b[i] = sc.nextInt();
		} b[i] = sc.nextInt() b[i] b i sc.nextInt() sc.nextInt sc sc.close() sc.close sc long ans = 0; ans 0 for (int i = n - 1; i >= 0; i--) {
			long val = Math.min(a[i + 1], b[i]);
			ans += val;
			b[i] -= val;
			val = Math.min(a[i], b[i]);
			ans += val;
			a[i] -= val;
		} int i = n - 1; int i = n - 1; i n - 1 n 1 i >= 0 i 0 i-- i-- i {
			long val = Math.min(a[i + 1], b[i]);
			ans += val;
			b[i] -= val;
			val = Math.min(a[i], b[i]);
			ans += val;
			a[i] -= val;
		} {
			long val = Math.min(a[i + 1], b[i]);
			ans += val;
			b[i] -= val;
			val = Math.min(a[i], b[i]);
			ans += val;
			a[i] -= val;
		} long val = Math.min(a[i + 1], b[i]); val Math.min(a[i + 1], b[i]) Math.min Math a[i + 1] a i + 1 i 1 b[i] b i ans += val ans val b[i] -= val b[i] b i val val = Math.min(a[i], b[i]) val Math.min(a[i], b[i]) Math.min Math a[i] a i b[i] b i ans += val ans val a[i] -= val a[i] a i val 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) throws Exception {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n + 1];
		int[] b = new int[n];
		for (int i = 0; i < n + 1; i++) {
			a[i] = sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			b[i] = sc.nextInt();
		}
		sc.close();

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

		long ans = 0;
		for (int i = n - 1; i >= 0; i--) {
			long val = Math.min(a[i + 1], b[i]);
			ans += val;
			b[i] -= val;
			val = Math.min(a[i], b[i]);
			ans += val;
			a[i] -= val;
		}
		System.out.println(ans);
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n + 1];
		int[] b = new int[n];
		for (int i = 0; i < n + 1; i++) {
			a[i] = sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			b[i] = sc.nextInt();
		}
		sc.close();

		long ans = 0;
		for (int i = n - 1; i >= 0; i--) {
			long val = Math.min(a[i + 1], b[i]);
			ans += val;
			b[i] -= val;
			val = Math.min(a[i], b[i]);
			ans += val;
			a[i] -= val;
		}
		System.out.println(ans);
	}
}
