import java.io.*;
import java.util.*;
public class Main
{
	public static void main(String args[])
	{
		Scanner x=new Scanner(System.in);
    	int n=x.nextInt();
		long c=0;
    	long a[]=new long[n+1];
		long b[]=new long[n];
		for(int i=0;i<n+1;i++)
		{
			a[i]=x.nextLong();
		}
		for(int i=0;i<n;i++)
		{
			b[i]=x.nextLong();
		}
		for(int i=0;i<n;i++)
		{
			c+=Math.min((a[i]+a[i+1]),b[i]);
			if(a[i]<b[i])
			{	
				b[i] -= a[i];
				if(a[i+1]>=b[i])
				{
				a[i+1]-=b[i];
				}
				else
				{
				a[i+1]=0;
				}
			}
		}
		System.out.println(c);
	}
}
/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