#include <iostream>
#include <vector>

using namespace std;

int main()
{
    int n,b,c,num=0,e,m = 0;
    cin >> n;
    vector<int> a;
    
    for(int d = 0;d<n-1;d++){
        cin >> e;
        a.push_back(e);
    }
    
    for(int d = 0;d<n-1;d++){
        cin >> b >> c;
        num += c - b;
        m += num*a[d];
    }
    
    cout << m << "\n";
   return -1;
}