#include <fstream>
using namespace std;
ifstream cin("branza.in");
ofstream cout("branza.out");
const int N=100001;
int v[N],dq[N];
int main()
{
    int n,s,t,i,st,dr;
    long long total=0;
    cin>>n>>s>>t;
    t++;
    st=0;
    dr=-1;
    for(i=0; i<n; i++)
    {
        int p;
        cin >> v[i] >> p;
        if (st <= dr && dq[st] == i-t)
        {
            st++;
        }
        while (st <= dr && v[i] <= v[dq[dr]] + s * (i-dq[dr]))
        {
            dr--;
        }
        dq[++dr]=i;
        total+=(long long)p*(v[dq[st]]+s*(i-dq[st]));
    }
    cout<<total;
    return 0;
}