#include <bits/stdc++.h>
using namespace std;
ifstream in("branza.in");
ofstream out("branza.out");
deque<pair<int,int>> q;
int n,s,t,i;
int x,y,sm;
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    in>>n>>s>>t;
    for(i=1;i<=n;++i)
    {
        in>>x>>y;
        while(!q.empty()&& q.front().second<i-t)
            q.pop_front();
        while(!q.empty() && q.back().first+s*(i-q.back().second)>=x)
            q.pop_back();
        q.push_back({x,i});
        sm+=y*(q.front().first+s*(i-q.front().second));
    }
    out<<sm;
}