import 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];
		for(int i=0; i<N+1; i++)
			A[i] = sc.nextInt();
		int[] B = new int[N];
		for(int i=0; i<N; i++)
			B[i] = sc.nextInt();

		long ans = 0;
		
		for(int i=0; i<N; i++) {
			int m1 = Math.min(A[i], B[i]);
			ans += m1;
			A[i] -= m1;
			B[i] -= m1;
			int m2 = Math.min(A[i+1], B[i]);
			ans += m2;
			A[i+1] -= m2;
			B[i] -= m2;
		}

		System.out.println(ans);
		sc.close();
	}
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz