#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define fi first
#define se second
#define all(a) a.begin(),a.end()
int main(){
  int a,b,c,d,e;
  cin >> a >> b >> c >> d >> e;
  int happy=a-b;
  if(d>e) happy+=c*(d-e);
  cout << happy << endl;
  return 0;
}