#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
ifstream f("branza.in");
ofstream g("branza.out");
const int N=1000001;
int d[N];
long long sum;
int n,s,t,st,dr=-1;
pair <int,int> v[N];
int main()
{
    f>>n>>s>>t;
    t++;
    for(int i=0;i<n;i++){
        f>>v[i].first>>v[i].second;
        if(st<=dr && d[st]==i-t)
           ++st;
        while(st<=dr && v[i].first <= v[d[dr]].first + s*(i - d[dr]))
           --dr;
        d[++dr]=i;
        sum+=v[i].second*(v[d[st]].first+s*(i - d[st]));
    }
    g<<sum;
    return 0;
}