import 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 = 0;
		for( int i=0; i<N; i++ ){
			if( B[i]<=A[i] ){
				ans += B[i];
			}else{
				if( B[i]<=A[i]+A[i+1] ){
					ans += B[i]; 
				}else{
					ans += A[i]+A[i+1];
				}
				A[i+1] -= B[i] - A[i];
				if( A[i+1]<0 ){
					A[i+1] = 0;
				}
			}
		}
		System.out.println(ans);
	}
}

/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