import java.util.*;

class Main{
public static void main(String[] args){
	long count = 0;
	Scanner scan = new Scanner(System.in);
	int num = scan.nextInt();//町の数
	long[] mons = new long[num+1];//n-1番目の街のモンスター数
	long[] yusya = new long[num];//n-1番目の勇者が倒せるモンスターの数
	for(int i = 0;i<num+1;i++){
		mons[i]=Long.parseLong(scan.next());
	}
	for(int i = 0;i<num;i++){
		yusya[i]=Long.parseLong(scan.next());
	}

	for(int i = 0;i<num;i++){
		if(mons[i]>=yusya[i])count+=yusya[i];
		else if((mons[i]+mons[i+1])<=yusya[i]){
			count+=mons[i]+mons[i+1];
			mons[i+1]=0;
		}else if(mons[i]<yusya[i]&&yusya[i]<(mons[i]+mons[i+1])){
			count+=yusya[i];
			mons[i+1]-=(yusya[i]-mons[i]);
		}
	}

	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