#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,f16c,fma,sse3,ssse3,sse4.1,sse4.2") 

#include <iostream>
#include <fstream>
#include <stack>

using namespace std;

int maxLen;
stack<pair<int,char>> st;

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

int cost[100000];
int quantity[100000];
int sum;

int main() {
    int n, s, t, c, p;
    myIn >> n >> s >> t;

    for (int i = 0; i < n; ++i) {
        myIn >> c >> p;
        cost[i] = c;
        quantity[i] = p;

        int costToday = cost[i] * quantity[i];
        //cout << "Day " << i << " before cost " << costToday << endl;
        for (int j = i; j >= max(0, i - t); --j) {
            costToday = min(costToday, s * (i - j) * quantity[i] + cost[j] * quantity[i]);
        }

        //cout << "Day " << i << " after cost " << costToday << endl;
        sum += costToday;
    }
    myOut << sum;
}

/*
(({}])
*/