#include <bits/stdc++.h>

using namespace std;

ifstream fin("branza.in");
ofstream fout("branza.out");

int n,s,t;

int c[100005];
int p[100005];

deque <int> dq;

int main()
{
    fin>>n>>s>>t;
    for(int i=1; i<=n; i++)
        fin>>c[i]>>p[i];
    long long ans=1LL*c[1]*p[1];
    for(int i=2; i<=n; i++)
    {
        while(!dq.empty() && dq.front()<i-t)
            dq.pop_front();
        while(!dq.empty() && c[dq.back()]+s*(i-dq.back())>c[i])
            dq.pop_back();
        dq.push_back(i);
        ans+=1LL*p[i]*(c[dq.front()]+s*(i-dq.front()));
    }
    fout<<ans<<"\n";
    return 0;
}