#include <iostream>
#include <fstream>
using namespace std;
ifstream in("branza.in");
ofstream out("branza.out");
const int N=100000;
int d[N], p[N], c[N];
int main()
{
    int n, t, i, dr=-1, st=0, s;
    long long m=0;
    in>>n>>s>>t;
    t++;
    for(i=0; i<n; i++)
    {
        in>>c[i]>>p[i];
        if (st<=dr && d[st]==i-t)
            st++;
        while(st<=dr && c[i] <= c[d[dr]] + (long long)s*(i-d[dr]))
            dr--;
        d[++dr]=i;
        m += p[i] * (c[d[st]]+(long long)s*(i-d[st]));
    }
    out<<m;
    return 0;
}