#include <iostream>
#include <vector>
#include <fstream>
#include <algorithm>
#include <cstring>
#include <deque>
//#define x first
//#define y second
using namespace std;
ifstream fin("branza.in");
ofstream fout("branza.out");
int n,m,ld,ls,mini,rasp,i,j,x[100001],y,z,d,v[100001],maxi,k,a,ok,b,nr;
deque < int > d1,d2;
long long int sum;

int main()
{
    fin>>n>>m>>b;
    for(i=1;i<=n;i++)
        fin>>v[i]>>x[i];
    for(i=1;i<=n;i++)
    {
        while( !d1.empty() && v[ d1.back() ] + ( i - d1.back() ) * m > v[ i ] )
            d1.pop_back();
        if(!d1.empty()&&d1.front()<=i-b)
            d1.pop_front();
        d1.push_back(i);
        sum+= v[d1.front()]*x[i] + (i-d1.front())*m*x[i];
    }
    fout<<sum;
return 0;
}