1

#include <iostream>
#include <vector>
#include <cmath>

using namespace std;

//ifstream cin("input.txt");
//ofstream cout("output.txt");
int main() {
    long long c, x, y, z, m, s, f, e, t;
    cin >> c >> x >> y >> z >> m >> s >> f >> e >> t;
    long long a = ceil((e + 1) * f / s) * m + t;
    long long n = ceil((c - x) / z);
    if (n < 0) {
        n = 0;
    }
    long long b = ceil((c + n * y) / s) * m;
    cout<<min(a, b);
    return 0;
}