#include <bits/stdc++.h>
using namespace std;
ifstream fin("branza.in");
ofstream fout("branza.out");
int c[100005];
int p[100005];
int v[100005];
deque<pair<int,int>> dq;
int main()
{
    int n,s,t,ans=0;
    fin>>n>>s>>t;
    for(int i=1;i<=n;i++)
    {
        fin>>c[i]>>p[i];
        v[i]=c[i]-s*i;
    }
    for(int i=1;i<=n;i++)
    {
        while(!dq.empty() && dq.back().first>v[i])
        {
            dq.pop_back();
        }
        while(!dq.empty() && dq.front().second<i-t+1)
        {
            dq.pop_front();
        }
        dq.push_back({v[i],i});
        ans+=(dq.front().first+i*s)*p[i];
    }
    fout<<ans;
    return 0;
}