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];
        long result = 0;
        for(int i=0; i<=N; i++){
          A[i]=sc.nextLong();
        }
        for(int i=0; i<N; i++){
          B[i]=sc.nextLong();
        }
        for(int i=0; i<N; i++){
           long d1 = Math.min(A[i], B[i]);
           result += d1;
           A[i] -= d1;
           B[i] -= d1;
 
           long d2 = Math.min(A[i+1], B[i]);
           result += d2;
           A[i+1] -= d2;
           B[i] -= d2;
        }
        System.out.println(result);
    }
}
/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