#include <iostream>
#include <fstream>
#include <set>
using namespace std;
ifstream in("branza.in");
ofstream out("branza.out");
const int maxn = 100005;
multiset <int> diff;
int C[maxn];
int P[maxn];
int main()
{
    int n, S, t;
    in >> n >> S >> t;
    for(int i = 1; i <= n; i++)
        in >> C[i] >> P[i];
    unsigned long long ans = 0;
    for(int i = 1; i <= n; i++)
    {
        diff.insert(C[i] - i * S);
        if(i > t)
            diff.erase(C[i - t] - (i - t) * S);
        int aux = *diff.begin();
        ans = ans + 1LL * P[i] * (i * S + aux);
    }
    out << ans << "\n";
    return 0;
}