#include <bits/stdc++.h>

using namespace std;
ifstream in("branza.in");
ofstream out("branza.out");
const int N = 1e5+5;
long long c[N],v[N],i;
int main()
{
    long long n,s,t,p,ans=0,st=0,dr=-1;
    in >> n >> s >> t;
    for (i = 1; i<=n; i++)
    {
        in >> c[i] >> p;
        if (v[st] == i-t-1)
            st++;
        while (st<=dr && c[i]<=c[v[dr]]+(i-v[dr])*s)
            dr--;
        v[++dr] = i;
        ans+=p*(c[v[st]]+(i-v[st])*s);
    }
    out << ans;
}