#include <fstream>
#include <deque>
#define nmax 10005
using namespace std;
ifstream f("branza.in");
ofstream g("branza.out");
int n,s,t,c[nmax],p[nmax];
long long sum;
deque <int > v;

int main()
{
    int i;
    f>>n>>s>>t;
    for (i=1;i<=n;i++) {
        f>>c[i]>>p[i];
    }
    for (i=1;i<=n;i++) {
        if (!v.empty()&&v.front()>t)
            v.pop_front();

        while (!v.empty()&&c[i]<1LL*c[v.back()]+(i-v.back())*1LL*s)
            v.pop_back();

        v.push_back(i);
        sum+=1LL*(c[v.front()]+(i-v.front())* 1LL*  s) * p[i];
    }
    g<<sum;
    return 0;
}