fn main() {
    let mut line = String::new();
    std::io::stdin().read_line(&mut line).unwrap();
    let a = line
        .split_whitespace()
        .map(|x| x.parse::<i32>().unwrap())
        .collect::<Vec<_>>();
    let (a, b, c, d, e) = (a[0], a[1], a[2], a[3], a[4]);
    let ans = a - b + c * (d - e).max(0);
    println!("{}", ans);
}