#include <iostream>
#include<fstream>
#include<deque>
#include<vector>
using namespace std;
ifstream f("branza.in");
ofstream g("branza.out");
int N,S,T,s=0,nr=0,i,x,y,b,ok=1,a;
//vector<int> C;
//vector<int> P;
int C[10000],P[10000];
deque<int> caut;
int main()
{
    f>>N>>S>>T;
    for(i=0;i<N;i++)
    {
        //f>>x>>y;
        //C.push_back(x);
        //P.push_back(y);
        f>>C[i]>>P[i];
        while(!caut.empty() && (C[i]<=C[caut.back()]+S*(i-caut.back())))
            caut.pop_back();
                caut.push_back(i);

        while((!caut.empty())&&(i-caut.front()>T))
            caut.pop_front();
        s+=(C[caut.front()]+S*(i-caut.front()))*P[i];

    }
    g<<s;
}