#include<bits/stdc++.h>
using namespace std;
ifstream f("branza.in");
ofstream g("branza.out");

long long n, s, t;

int main()
{
    long long c, p, suma=0;
    vector <pair <long long, long long>> vect;
    deque <long long> deq;
    f>>n>>s>>t;
    for(long long i=0; i<n; i++) {
        f >> c >> p;
        vect.push_back(pair<long long, long long>(c, p));
        while (deq.empty() == 0 && i - deq.front() - 1 == t) {
            deq.pop_front();
        }
        while (deq.empty() == 0 && c <= vect[deq.back()].first + (i - deq.back()) * s) {
            deq.pop_back();
        }
        deq.push_back(i);
        suma += (vect[deq.front()].first + (i - deq.front()) * s) * p;
    }
    g<<suma;
    return 0;



    }