#include<bits/stdc++.h>
using namespace std;
long long m,a[10010],b[10010],dp[10010],ans=1e18,min1;
inline long long read()
{
    long long x=0,f=1;
    char ch=getchar();
    while(ch<'0'||ch>'9')
    {
        if(ch=='-')
            f=-1;
        ch=getchar();
    }
    while(ch>='0' && ch<='9')
        x=x*10+ch-'0',ch=getchar();
    return x*f;
}
int main()
{
	m=read();
	for(int i=1;i<=m;++i)
	{
		a[i]=read();
	}
	for(int i=1;i<=m;++i)
	{
		b[i]=read();
	}
	dp[1]=a[1];
	for(int i=2;i<=m;++i)
	{
		dp[i]=dp[i-1]+a[i]+min(b[i],b[i-1]);
	}
	cout<<dp[m]<<endl;
}