#include <fstream>

using namespace std;

ifstream cin("branza.in");
ofstream cout("branza.out");
int d[100001],v[100001],c[100001];
int main()
{
    int n,s,t,i,st =0,dr=-1;
    cin >> n >> s >> t;
    t++;
    long long sum = 0;
    for(i=0; i<n; i++)
    {
        cin  >> v[i] >> c[i];

        if(st<=dr && d[st] == i-t)
        {
            st++;
        }
        while(st<=dr && v[i] <= v[d[dr]] + s * (i - d[dr])){
              dr--;
        }
        d[++dr] = i;
        sum = sum +  c[i] * (v[d[st]] + ((long long)s * (i - d[st])));

    }
    cout << sum;
    return 0;
}