#include <bits/stdc++.h>
#define REP(i, a, n) for(ll i=a; i<n; i++)
#define RREP(i, a, n) for(ll i=n-1; i>=a; i--)
typedef long long ll;
const ll mod =1e9+7;
const ll inf =1e18;
using namespace std;

ll n;
ll a[101], b[101], c[101];
int main() {
    cin>>n;
    REP(i, 0, n-1) cin>>a[i];
    REP(i, 0, n) cin>>b[i]>>c[i];

    ll ans=0;
    ll person=c[0];
    REP(i, 1, n){
        ans+=person*a[i-1];
        person-=b[i];
        person+=c[i];
    }
    cout<<ans<<endl;
    return 0;
}