fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let s: Vec<u32> = s.split_whitespace().flat_map(str::parse).collect();

    let n = (s[1] - s[2]) * s[0];
    let mut x = s[3];
    let mut ans = 0;
    for i in 1..=n {
        if i % 10 == 0 && s[4] <= x {
            x -= s[4];
        }
        ans += x;
    }
    println!("{}", ans);
}