#include <bits/stdc++.h>

using namespace std;
typedef unsigned long long int ulli;
struct dragon{
    ulli days, bills;
    int arrival_day;
    int training_day;
};

const bool operator < (const dragon a, const dragon b) {
    return a.bills*b.days < a.days*b.bills;
}

int main()
{
    priority_queue <dragon> dragons;
    unsigned long long int ans=0;
    unsigned long long int d,b;
    scanf("%llu %llu",&d,&b);
    dragon current_dragon;
    current_dragon.days=d;
    current_dragon.bills=b;
    current_dragon.arrival_day=0;
    current_dragon.training_day=0;
    int current_day=0;
    current_day++;
    while(scanf("%llu %llu",&d,&b)!=EOF){
        dragon a;
        a.days = d;
        a.bills = b;
        a.arrival_day = current_day;
        dragons.push(a);
        if(current_day - current_dragon.training_day == current_dragon.days){
            current_dragon = dragons.top();
            dragons.pop();
            current_dragon.training_day = current_day;
            ans += (current_dragon.training_day-current_dragon.arrival_day)*(current_dragon.bills);
        }
        current_day++;
    }
    while(!dragons.empty()){
        if(current_day - current_dragon.training_day == current_dragon.days){
            current_dragon = dragons.top();
            dragons.pop();
            current_dragon.training_day = current_day;
            ans += (current_dragon.training_day-current_dragon.arrival_day)*(current_dragon.bills);
        }
        current_day++;
    }
    printf("%llu\n",ans);
    return 0;
}