#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = unsigned;
using u64 = unsigned long long;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max() / 32 * 15 + 208;

int main() {
    int a, b, c, d, e;
    cin >> a >> b >> c >> d >> e;
    int n = a*(b-c), p = d, ans = 0;
    for (int i = 2; i <= n+1; ++i) {
        ans += p;
        if(p >= e && i%10 == 0) p -= e;
    }
    cout << ans << "\n";
    return 0;
}