#include <iostream>
#include <fstream>

using namespace std;

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

const int N = 100000;

int c[N],d[N];

int main()
{
    int n,s,t,st=0,dr=-1,x;
    long long q=0;
    fin>>n>>s>>t;
    t++;
    for(int i=0;i<n;i++){
        fin>>c[i]>>x;
        if(st<=dr&&d[st]==i-t){
            st++;
        }
        while(st<=dr&&c[i]<=c[d[dr]]+s*(i-d[dr])){
            dr--;
        }
        d[++dr]=i;
        q+=(c[d[st]]+(long long)s*(i-d[st]))*x;
    }
    fout<<q;
    return 0;
}