#include<iostream>
#include<cstdio>

using namespace std;

const int N = 10010;

int n;
int a[N], b[N];
long long ans;

int main(){

    scanf("%d", &n);
    for(int i = 1; i <= n; i++){
        scanf("%d", &a[i]);
        ans += a[i];
    }
    for(int i = 1; i <= n; i++){
        scanf("%d", &b[i]);
    }

    for(int i = 2; i <= n; i++){
        ans += min(b[i], b[i-1]);
    }

    printf("%lld\n", ans);

    return 0;
}