import java.io.*;
import java.util.*;
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
      	PrintWriter out = new PrintWriter(System.out);
      	int N = sc.nextInt();
      	int[] monsters = new int[N + 1];
      	int[] strength = new int[N];
      	for (int i = 0; i < N + 1; i++) {
        	monsters[i] = sc.nextInt(); 
        }
      	for (int i = 0; i < N; i++) {
        	strength[i] = sc.nextInt(); 
        }
      	long total = 0;
      	for (int i = N - 1; i >= 0; i--) {
          	int killedFirst = Math.min(monsters[i + 1], strength[i]);
          	strength[i] -= killedFirst;
          	int killedSecond = Math.min(strength[i], monsters[i]);
          	monsters[i] -= killedSecond;
          	total += (killedFirst + killedSecond);
        }
      	out.println(total);
      	out.close();
    }
}
/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