import java.util.*;
 
public class Main {
	public static void main (String[] args) {
		Scanner in = new Scanner(System.in);		
		int N = in.nextInt();
        long mo[] = new long[N+1];
      
      for(int i = 0;i < N+1;i++){
      	mo[i] = in.nextInt(); 
      }
      
      long sum = 0;
      long yu = 0;
      
      for(int i =0;i < N;i++){
		yu = in.nextInt(); 
        
        if(yu>mo[i]){
        	sum += mo[i];
            yu  -= mo[i]; 
        	sum += Math.min(mo[i+1],yu);
            mo[i+1] = Math.max(0,mo[i+1]-yu); 
        }else{
          sum +=yu;
        }
      }
       System.out.print(sum); 
      }
	}
/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