import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int N = sc.nextInt();
		int[] numMonsters = new int[N+1];
		int[] capasityHero = new int[N];		
		for(int i=0;i<N+1;i++) {
			numMonsters[i] = sc.nextInt();
		}		
		for(int i=0;i<N; i++) {
			capasityHero[i] = sc.nextInt();
		}
		
		long sum = 0;
		for(int i=0;i<N;i++) {
			sum += Math.min(numMonsters[i], capasityHero[i]);
			int extra = Math.max(0, capasityHero[i] - numMonsters[i]);
			sum += Math.min(numMonsters[i+1], extra);
			numMonsters[i+1] =  Math.max(0, numMonsters[i+1] - extra);
		}
		
		System.out.println(sum);
		
		sc.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