#include <iostream>
#include <fstream>

using namespace std;

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

int c[100001], d[100001];

int main()
{
    int n, s, t, i, st=0, dr=-1, p;
    long long sum=0;
    in >> n >> s >> t;
    for(i=0; i<n; i++){
        in >> c[i] >> p;
        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;
        sum += p* ( c[d[st]] + (long long)s*(i-d[st]) );
    }
    out << sum;
    return 0;
}