#include <bits/stdc++.h>

using namespace std;
deque <int> d;
int n,t,s,c[100005],p[100005],i,j,cmin;
long long cnt;
int main()
{
    cin>>n>>s>>t;
    for (i=1;i<=n;i++)
            cin>>c[i]>>p[i];
    d.push_front(1);
    for (i=1;i<=n;i++)
        {
            while (!d.empty() && c[i]<((i-d.front())*s+c[d.front()])) q.pop_front();
            q.pop_back(i);
            cnt+=(long long)(((i-d.front())*s+c[d.front()]))*p[i];
        }
    return 0;
}