#include <iostream>
#include <fstream>
#include <deque>
using namespace std; ifstream fin("branza.in"); ofstream fout("branza.out");
const int N = 1e5 + 1; long long v[N], qt[N]; deque <long long> deq;
int main(){long long n, s, t, i, total; fin >> n >> s >> t; for(i = 0; i < n; i++) fin >> v[i] >> qt[i]; total = 0; t++; for(i = 0; i < n; i++){
        if(!deq.empty() && deq.front() == i - t) deq.pop_front(); while(!deq.empty() && s * (i - deq.back()) + v[deq.back()] >= v[i]) deq.pop_back();
        deq.push_back(i); total += qt[i] * (v[deq.front()] + s * (i - deq.front())); } fout << total; return 0;}