import java.util.*;
 
public class Main {
  public static void main (String[] arg) {
    Scanner scan = new Scanner(System.in);
    int N = scan.nextInt();
    long A[] = new long[N+1];
    long B[] = new long[N];
    long Kc = 0;

    for (int i = 0; i < N+1; i++){
      A[i] = scan.nextLong();
    }

    for (int i = 0; i < N; i++){
      B[i] = scan.nextLong();
    }
    
    for(int i = 0; i < N; i++){
      if(B[i] > A[i]){
        B[i] -= A[i];
        Kc += A[i];
        if(B[i] > A[i+1]){
          Kc += A[i+1];
          A[i+1] = 0;
        } else {
          Kc += B[i];
          A[i+1] -= B[i];
        }
      } else {
        Kc += B[i];
      }
    }
    System.out.println(Kc);
  }
}
/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