#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, e) for (int i = (int)(s); i < (int)(e); ++i)
#define all(a) (a).begin(),(a).end()

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    
    int A, B, C, D, E;
    cin >> A >> B >> C >> D >> E;
    
    int need = (B - C)*A;
    ll ans = 0;
    ll prev = D;
    rep(i, 2, need + 2) {
        ans += prev;
        if (i % 10 == 0 && E <= prev) prev -= E;
    }
    cout << ans << '\n';
}