#include <bits/stdc++.h>
#define dim 100003
using namespace std;

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

long long v[dim];

int main() {
    long long n, s, t, c, p, min, suma = 0;

    fin >> n >> s >> t;

    fin >> c >> p;
    v[0] = c;
    suma += c * p;

    for(int k = 1; k < n; k++) {
        fin >> c >> p;
        v[k] = c;
        min = c;

        for(int i = 1; i <= t && k - i >= 0; i++)
            if( v[k - i] + s * i < min )
                min = v[k - i] + s * i;

        suma += p * min;
    }

    fout << suma;

    return 0;
}