#include<bits/stdc++.h> 
using namespace std;
int main()
{ 
  int n,m,x,t,d;
  cin>>n>>m>>x>>t>>d;
  if(m>=x)
  { 
    cout<<t; 
  }
  else
  { 
  cout<<t-(x-m)*d;
  }
  return 0;
}