#include <iostream>
#include <string>
#include <vector>
#include <set>
#include <cstdio>
#include <algorithm>
#include <functional>
#include <map>

using namespace std;

int a[200];
int b[200];
int c[200];

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    int answer=0;
    int n;scanf("%d",&n);

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

    int people=c[1];
    for(int i=1;i<=n-1;i++){
        int money=people*a[i];
        answer+=money;
        people-=b[i+1];
        people+=c[i+1];
    }

    printf("%d\n",answer);

    return 0;
}