#include <bits/stdc++.h>

using namespace std;

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

deque <int> v;
long long cost,c[100001];

int main()
{
    long long n,s,t,p,i,j;

    f>>n>>s>>t;

    for(i=1;i<=n;++i){
        f>>c[i]>>p;

        while(!v.empty() && c[v.back()]+s*(i-v.back())>c[i])
            v.pop_back();
        while(!v.empty() && i-v.front()>t)
            v.pop_front();
        v.push_back(i);

        cost+=(c[v.front()]+s*(i-v.front()))*p;
    }

    g<<cost;

    return 0;
}