import java.util.*;
import static java.lang.System.*;

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];
	  int[] B = new int[N];
	  long count = 0;  
	  for(int i=0; i<N+1; i++) {
		  A[i] = sc.nextInt();
	  }
	  for(int i=0; i<N; i++) {
		  B[i] = sc.nextInt();
	  }
	  
	  for(int i=0; i<N; i++) {
		  int n = Math.min(A[i], B[i]);
		  count += n;
		  B[i] -= n;
		  A[i] -= n;
		  int m = Math.min(A[i+1], B[i]);
		  count += m;
		  A[i+1] -= m;
	  }
	  out.println(count);  
	  
  }
}
/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