import java.util.Scanner;

public class Main {
  public static void main (String[] args) {
    Scanner in = new Scanner(System.in);

    while (in.hasNext()) {
      int N = in.nextInt();
      int[] A = new int[N + 1];
      int[] B = new int[N];
      long killed = 0;

      for (int i = 0; i < A.length; ++i) {
        A[i] = in.nextInt();
      }

      for (int i = 0; i < B.length; ++i) {
        B[i] = in.nextInt();
      }

      for (int i = 0; i < B.length; ++i) {
        int areaSum = A[i] + A[i + 1];

        killed += Math.min(B[i], areaSum);
        
        B[i] = Math.max(B[i] - A[i], 0);
        A[i + 1] = Math.max(A[i + 1] - B[i], 0);
      }

      System.out.println(killed);
    }
  }
}
/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