/**
 *   @FileName	a.cpp
 *   @Author	kanpurin
 *   @Created	2022.10.17 02:34:36
**/

#include "bits/stdc++.h" 
using namespace std; 
typedef long long ll;


constexpr long long LLINF = 1e18 + 1;

int main() {
    int t;cin >> t;
    int x,a,y,b;cin >> x >> a >> y >> b;
    ll ans = LLINF;
    for (int i = 0; i <= 10000000; i++) {
        ll j = max(0LL,((ll)a*i-t+b-1)/b);
        ans = min(ans,(ll)(x-a)*i+(y+b)*j+t);
    }
    cout << ans << endl;
    return 0;
}