#include <iostream>
#include <fstream>
#include <stack>
#include <vector>
#include <queue>

using namespace std;
ifstream in("branza.in");
ofstream out("branza.out");

#define ll long long
#define ull unsigned long long
#define pb push_back
const int inf = 1e9 + 5;
const int NMax = 1e5 + 5;

int N,S,T;

struct elem {
    int week,val;
    elem(int _week = 0,int _val = 0) {
        week = _week;
        val = _val;
    }
};
deque<elem> deq;

int main() {
    in>>N>>S>>T;

    ll ans = 0;
    for (int i=1;i <= N;++i) {
        int c,p;
        in>>c>>p;

        while (deq.size() && deq.back().val + 1LL * (i-deq.back().week) * S >= c) {
            deq.pop_back();
        }
        deq.push_back(elem(i,c));
        if (deq.front().week < i-T) {
            deq.pop_front();
        }

        ans += (1LL*deq.front().val + 1LL*(i-deq.front().week)*S) * p;
    }
    out<<ans<<'\n';

    in.close();out.close();
    return 0;
}