#include <iostream>
using namespace std;

int main()
{long n, s, t,i, j, s1, poz, c[1000001], p[1000001];
long long sol;
cin>>n>>s>>t;
for(i=1; i<=n; i++)
{
    cin>>c[i]>>p[i];
}
i=1;
while(i<=n)
{
    if(c[poz]+s1<c[i+1])
    {j=1;
    s1=s;
    poz=i;
    while(i<=n && c[poz]+s1<c[i+1] && j<=t)
    {
        j++;
        sol=sol+c[i]+s1;
        s1=s1+s;
        i++;
    }
    }
    else
    {
        sol=sol+c[i]+s;
        i++;
    }
}
    cout << sol<< endl;
    return 0;
}