#include <bits/stdc++.h>

using namespace std;
int v[100005],d[100005];
ifstream fin("branza.in");
ofstream fout("branza.out");
int n,s,t,i,c,pr;
long long sol;
int main()
{
    fin>>n>>s>>t;
    int u,p;
    u=p=1;
    d[1]=1;
    for(i=1;i<=n;i++)
    {
        fin>>c>>pr;
        v[i]=c;
        while(p<=u&&v[d[u]]+(i-d[u])*s>=c)u--;
        d[++u]=i;
        sol+=((long long)v[d[p]]+(long long)(i-d[p])*s)*pr;
        if(i-d[p]==t)p++;
    }
    fout<<sol;
    return 0;
}