#include <bits/stdc++.h>

using namespace std;

ifstream in("branza.in");
ofstream out("branza.out");

int main()
{
    
    int n,s,t;
    in>>n>>s>>t;
    unsigned long long CM=0;
    deque<pair<int, int>> minime;
    for(int i=0; i<n; i++)
    {
        int c,p;
        in>>c>>p;
        while(!minime.empty() && (minime.back().second)+(i-minime.back().first)*s>=c)
            minime.pop_back();
        pair<int, int> cost;
        cost.first=i; cost.second=c;
        minime.push_back(cost);
        if(minime.front().first<i-t)
            minime.pop_front();
        CM+=(unsigned long long)(minime.front().second+(i-minime.front().first)*s)*p;
    }
    out<<CM;
    return 0;
}