#include <bits/stdc++.h>

using namespace std;
ifstream f("branza.in");
ofstream g("branza.out");
long long n,s,t,i,sum,cost[100005],cant[100005];
deque <long long > d;
int main()
{
    f>>n>>s>>t;
    for (i=1;i<=n;i++)
    {
        f>>cost[i]>>cant[i];
        while (!d.empty()&&cost[d.back()]+s*(i-d.back())>cost[i])
        {
            d.pop_back();
        }
        d.push_back(i);
        if (!d.empty()&&d.front()+t<i)
        {
            d.pop_front();
        }
        sum=sum+((i-d.front())*s+cost[d.front()])*cant[i];
    }
    g<<sum;
    return 0;
}