#include <iostream>
#include <fstream>
using namespace std;

const long long N=100000;
long long c[N],p[N],d[N];

int main()
{
    ifstream fin ("branza.in");
    ofstream fout ("branza.out");
    long long st=0, dr=-1, n, t, s;
    long long C=0;
    fin>>n>>s>>t;
    for(int i=0; i<n; i++)
    {
        fin>>p[i]>>c[i];
        if(st<=dr&&d[st]==i-t)
            st++;
        while(st<=dr&&(i-d[dr])*s+p[d[dr]]>=p[i])
            dr--;
        d[++dr]=i;
        if(i==d[st]) C+=p[i]*c[i];
        else C+=c[i]*((i-d[st])*s+p[d[st]]);
    }
    fout<<C;
    return 0;
}