#![allow(non_snake_case)]

use std::io::{ self, prelude::* };

macro_rules! pick {
    ($tokens:expr) => {
        $tokens.next().unwrap().parse().expect("parse error")
    }
}

fn main() {
    let mut s = String::new();
    io::stdin().read_to_string(&mut s).expect("i/o error");
    let mut tokens = s.split_whitespace();

    let b1: i64 = pick!(tokens);
    let b2: i64 = pick!(tokens);
    let b3: i64 = pick!(tokens);

    let b4 = b3*(b2-b3)/(b1-b2) + (b2 - b1*(b2-b3)/(b1-b2));

    println!("{}", b4);
}