#include <fstream>
#include <deque>
#include <iostream>

using namespace std;

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

deque < long long int > d;
long long int i,j,k,n,l,m,v[100010],s,t,x,ans;

int main()
{
    fin>>n>>s>>t;
    for( i = 1 ; i <= n ; i++ )
    {
        fin>>v[ i ]>>x;

        while( d.size() && v[ d.back() ] + s * ( i - d.back() ) > v[ i ] )
        {
            d.pop_back();
        }
        d.push_back( i );

        if( d.front() < i - t )
            d.pop_front();
        ans += ( v[ d.front() ] + s * ( i - d.front() ) ) * x;
    }
    fout<<ans;
}