#include<iostream>
#include<string>
#include<algorithm>
#include<cctype>
#include<set>
#include<bitset>
#include<math.h>
#include<map>
#include<queue>
#include <iomanip>
using namespace std;

int main(){
    map<string, int> CodeC;
    int a, b, c, d, e;
    cin >> a >> b >> c >> d >> e;
    if (d >= e) cout << a - b + (d - e) * c << endl;
    else cout << a - b << endl;
}