#include <bits/stdc++.h>
#define LL long long

using namespace std;

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

LL n,s,t,cost,cant,minn;
deque<pair<LL,LL>> dq;

int main() {
    fin>>n>>s>>t;
    for(int i=0;i<n;i++){
        fin>>cost>>cant;
        while(!dq.empty() && cost <= dq.back().second + s*(i-dq.back().first))
            dq.pop_back();
        dq.push_back(make_pair(i,cost));
        if(dq.front().first < i-t)
            dq.pop_front();
        minn += cant*(dq.front().second + s * (i-dq.front().first));
    }

    fout<<minn;
    return 0;
}