#include <iostream>
#include <fstream>
#define MAX_N 100001
using namespace std;
int d[MAX_N],first,last;
long C[MAX_N],P[MAX_N],n,t;
long long total;
int s;
void citeste()
{
    ifstream f("branza.in");
    f>>n>>s>>t;
    for(int i=1;i<=n;i++)
        f>>C[i]>>P[i];
    f.close();
}
int main()
{
    citeste();
    first=1;
    for(int i=1;i<=n;i++)
    {
        while(first<=last&&C[i]<C[d[last]]+(i-d[last])*s)last--;
        d[++last]=i;
        if(d[first]==i-t)first++;
        total+=(C[d[first]]+(i-d[first])*s)*P[i];
    }
    ofstream g("branza.out");
    g<<total;
    g.close();
    return 0;
}