#include <iostream>
#include <fstream>

using namespace std;

ifstream f ("branza.in");
ofstream g("branza.out");

int n,t,c,dq[100000],v[10000000],st,dr,s,p[10000000];
long long S;
int main()
{
    int i;

    f>>n>>s>>t;
    for(i=0; i<n; i++)
        f>>v[i]>>p[i];
    t++;
    st=0;
    dr=-1;

    for(i=0; i<n; i++)
    {
        if(dq[st] == i-t)
            st++;

        while(st <= dr && v[i] <= (v[dq[dr]] + (i-dq[dr])*s) )
            dr--;

        dq[++dr]=i;

        S=S+p[i]*(v[dq[st]]-s*(i-dq[st]));

    }
    cout<<S;
    return 0;
}