#include <bits/stdc++.h>

using namespace std;
ifstream fin("branza.in");
ofstream fout("branza.out");
deque <int> d;
long long n,t,s,c[100005],p[100005],i,j,cmin;
long long cnt;
int main()
{
    fin>>n>>s>>t;
    for (i=1;i<=n;i++)
            fin>>c[i]>>p[i];
    d.push_front(1);
    for (i=2;i<=n;i++)
        {
            while (!d.empty() && c[i]<((i-d.front())*s+c[d.front()])) d.pop_front();
            d.push_back(i);
            cnt+=(long long)((((i-d.front())*s+c[d.front()]))*p[i]);
            if (!d.empty() && d.front()==i-t) d.pop_front();
        }
    fout<<cnt;
    return 0;
}