#include <bits/stdc++.h>

using namespace std;

ifstream fin("branza.in");
ofstream fout("branza.out");
int n, s, t, c[1002], kg[1002], i, r;
deque<int> q;

int main() {
    fin >> n >> s >> t;
    for(i = 1; i <= n; i++) fin >> c[i] >> kg[i];
    for(i = 1; i <= n; i++) {
        if(i > t + q.front()) q.pop_front();
        while(!q.empty() && c[i] <= c[q.back()] + s * (i - q.front())) q.pop_back();
        q.push_back(i);
        r += kg[i] * s * (i - q.front()) + kg[i] * c[q.front()];
    }
    fout << r;

    return 0;
}