#define _DE123BUG
#include <bits/stdc++.h>
using namespace std;
#define endl "\n"
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const long double pi = acos(-1.0);
const int INF = 1987654321;
// const int MOD = 1e9;
////


int main(){
#ifdef _DEBUG
    freopen ("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif  
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    
    ll a, b, c, d, e; cin >> a >> b >> c >> d >> e;
    if(d < e) cout << a - b << endl;
    else cout << a-b + c * (d-e) << endl;
                
    return 0;
}