#include <bits/stdc++.h>

using namespace std;

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

int n, s, t, c, p[100002];
long long ans;
deque<int> a;

int main()
{
    f>>n>>s>>t;
    for(int i=1; i<=n; i++)
    {
        if(!a.empty() && a.front()<=i-t-1) a.pop_front();
        f>>p[i]>>c;
        while(!a.empty() && p[a.back()]+s*(i-a.back())>=p[i]) a.pop_back();
        a.push_back(i);
        ans=ans+(long long)c*(p[a.front()]+s*(i-a.front()));
    }
    g<<ans;
    return 0;
}