#include <iostream>
#include <fstream>

using namespace std;

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

const int N = 100001;
int v[N],d[N];

int main()
{
    int n,s,t,st,dr,i,p;
    long long sum = 0;
    in >> n >> s >> t;
    st = 0;
    dr = -1;
    t++;
    for(i = 1 ; i <= n ; i++){
        in >> v[i] >> p;
        while(st <= dr && v[i] <= v[d[dr]] + (long long)s * (i - d[dr])){
            dr--;
        }
        d[++dr] = i;
        sum += (v[d[st]] + (long long)s * (i - d[st])) * p;

    }
    out<<sum;

    return 0;
}