import java.util.*;
import java.math.*;
class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();
        long[] cities = new long[num+1];
        long[] heroes = new long[num];
        for(int i=0;i<num+1;i++)
            cities[i]=sc.nextLong();
        for(int i=0;i<num;i++)
            heroes[i]=sc.nextLong();
        long count=0;
        long x=0;
        for(int i=0;i<num;i++)
        {
            x = Math.min(cities[i], heroes[i]);
            heroes[i] -= x;
            count += x;
            x = Math.min(cities[i+1], heroes[i]);
            cities[i+1] -= x;
            count += x;
        }
        System.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