import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		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();
		}

		long sum = 0;

		for (int i = 0; i < n; i++) {
			int tmp = b[i];
			sum += Math.min(a[i], b[i]);
			b[i] = Math.max(b[i] - a[i], 0);
			a[i] = Math.max(a[i] - tmp, 0);

//			System.out.println(i + "->" + i + ", a:" + a[i] + ", b:" + b[i]);

			sum += Math.min(a[i + 1], b[i]);
			a[i + 1] = Math.max(a[i + 1] - b[i], 0);
//			System.out.println(i + "->" + (i + 1) + ", a+1:" + a[i + 1]);
		}
		System.out.println(sum);
		sc.close();
	}
} 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();
		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();
		}

		long sum = 0;

		for (int i = 0; i < n; i++) {
			int tmp = b[i];
			sum += Math.min(a[i], b[i]);
			b[i] = Math.max(b[i] - a[i], 0);
			a[i] = Math.max(a[i] - tmp, 0);

//			System.out.println(i + "->" + i + ", a:" + a[i] + ", b:" + b[i]);

			sum += Math.min(a[i + 1], b[i]);
			a[i + 1] = Math.max(a[i + 1] - b[i], 0);
//			System.out.println(i + "->" + (i + 1) + ", a+1:" + a[i + 1]);
		}
		System.out.println(sum);
		sc.close();
	}
} Main public static void main(String[] args) {

		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();
		}

		long sum = 0;

		for (int i = 0; i < n; i++) {
			int tmp = b[i];
			sum += Math.min(a[i], b[i]);
			b[i] = Math.max(b[i] - a[i], 0);
			a[i] = Math.max(a[i] - tmp, 0);

//			System.out.println(i + "->" + i + ", a:" + a[i] + ", b:" + b[i]);

			sum += Math.min(a[i + 1], b[i]);
			a[i + 1] = Math.max(a[i + 1] - b[i], 0);
//			System.out.println(i + "->" + (i + 1) + ", a+1:" + a[i + 1]);
		}
		System.out.println(sum);
		sc.close();
	} 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();
		}

		long sum = 0;

		for (int i = 0; i < n; i++) {
			int tmp = b[i];
			sum += Math.min(a[i], b[i]);
			b[i] = Math.max(b[i] - a[i], 0);
			a[i] = Math.max(a[i] - tmp, 0);

//			System.out.println(i + "->" + i + ", a:" + a[i] + ", b:" + b[i]);

			sum += Math.min(a[i + 1], b[i]);
			a[i + 1] = Math.max(a[i + 1] - b[i], 0);
//			System.out.println(i + "->" + (i + 1) + ", a+1:" + a[i + 1]);
		}
		System.out.println(sum);
		sc.close();
	} 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 long sum = 0; sum 0 for (int i = 0; i < n; i++) {
			int tmp = b[i];
			sum += Math.min(a[i], b[i]);
			b[i] = Math.max(b[i] - a[i], 0);
			a[i] = Math.max(a[i] - tmp, 0);

//			System.out.println(i + "->" + i + ", a:" + a[i] + ", b:" + b[i]);

			sum += Math.min(a[i + 1], b[i]);
			a[i + 1] = Math.max(a[i + 1] - b[i], 0);
//			System.out.println(i + "->" + (i + 1) + ", a+1:" + a[i + 1]);
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			int tmp = b[i];
			sum += Math.min(a[i], b[i]);
			b[i] = Math.max(b[i] - a[i], 0);
			a[i] = Math.max(a[i] - tmp, 0);

//			System.out.println(i + "->" + i + ", a:" + a[i] + ", b:" + b[i]);

			sum += Math.min(a[i + 1], b[i]);
			a[i + 1] = Math.max(a[i + 1] - b[i], 0);
//			System.out.println(i + "->" + (i + 1) + ", a+1:" + a[i + 1]);
		} {
			int tmp = b[i];
			sum += Math.min(a[i], b[i]);
			b[i] = Math.max(b[i] - a[i], 0);
			a[i] = Math.max(a[i] - tmp, 0);

//			System.out.println(i + "->" + i + ", a:" + a[i] + ", b:" + b[i]);

			sum += Math.min(a[i + 1], b[i]);
			a[i + 1] = Math.max(a[i + 1] - b[i], 0);
//			System.out.println(i + "->" + (i + 1) + ", a+1:" + a[i + 1]);
		} int tmp = b[i]; tmp b[i] b i sum += Math.min(a[i], b[i]) sum Math.min(a[i], b[i]) Math.min Math a[i] a i b[i] b i b[i] = Math.max(b[i] - a[i], 0) b[i] b i Math.max(b[i] - a[i], 0) Math.max Math b[i] - a[i] b[i] b i a[i] a i 0 a[i] = Math.max(a[i] - tmp, 0) a[i] a i Math.max(a[i] - tmp, 0) Math.max Math a[i] - tmp a[i] a i tmp 0 sum += Math.min(a[i + 1], b[i]) sum 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] = Math.max(a[i + 1] - b[i], 0) a[i + 1] a i + 1 i 1 Math.max(a[i + 1] - b[i], 0) Math.max Math a[i + 1] - b[i] a[i + 1] a i + 1 i 1 b[i] b i 0 System.out.println(sum) System.out.println System.out System System.out sum sc.close() sc.close sc String[] args args public class Main {

	public static void main(String[] args) {

		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();
		}

		long sum = 0;

		for (int i = 0; i < n; i++) {
			int tmp = b[i];
			sum += Math.min(a[i], b[i]);
			b[i] = Math.max(b[i] - a[i], 0);
			a[i] = Math.max(a[i] - tmp, 0);

//			System.out.println(i + "->" + i + ", a:" + a[i] + ", b:" + b[i]);

			sum += Math.min(a[i + 1], b[i]);
			a[i + 1] = Math.max(a[i + 1] - b[i], 0);
//			System.out.println(i + "->" + (i + 1) + ", a+1:" + a[i + 1]);
		}
		System.out.println(sum);
		sc.close();
	}
} public class Main {

	public static void main(String[] args) {

		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();
		}

		long sum = 0;

		for (int i = 0; i < n; i++) {
			int tmp = b[i];
			sum += Math.min(a[i], b[i]);
			b[i] = Math.max(b[i] - a[i], 0);
			a[i] = Math.max(a[i] - tmp, 0);

//			System.out.println(i + "->" + i + ", a:" + a[i] + ", b:" + b[i]);

			sum += Math.min(a[i + 1], b[i]);
			a[i + 1] = Math.max(a[i + 1] - b[i], 0);
//			System.out.println(i + "->" + (i + 1) + ", a+1:" + a[i + 1]);
		}
		System.out.println(sum);
		sc.close();
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		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();
		}

		long sum = 0;

		for (int i = 0; i < n; i++) {
			int tmp = b[i];
			sum += Math.min(a[i], b[i]);
			b[i] = Math.max(b[i] - a[i], 0);
			a[i] = Math.max(a[i] - tmp, 0);

//			System.out.println(i + "->" + i + ", a:" + a[i] + ", b:" + b[i]);

			sum += Math.min(a[i + 1], b[i]);
			a[i + 1] = Math.max(a[i + 1] - b[i], 0);
//			System.out.println(i + "->" + (i + 1) + ", a+1:" + a[i + 1]);
		}
		System.out.println(sum);
		sc.close();
	}
}