Problem:
Score : 400 points

Problem Statement

Given are integers A, B, and N.

Find the maximum possible value of floor(Ax/B) - A × floor(x/B) for a non-negative integer x not greater than N.

Here floor(t) denotes the greatest integer not greater than the real number t.

Constraints

1 ≤ A ≤ 10^{6}

1 ≤ B ≤ 10^{12}

1 ≤ N ≤ 10^{12}

All values in input are integers.

Input

Input is given from Standard Input in the following format:

A B N

Output

Print the maximum possible value of floor(Ax/B) - A × floor(x/B) for a non-negative integer x not greater than N, as an integer.

Sample Input 1

5 7 4

Sample Output 1

2

When x=3, floor(Ax/B)-A×floor(x/B) = floor(15/7) - 5×floor(3/7) = 2. This is the maximum value possible.

Sample Input 2

11 10 9

Sample Output 2

9

Solution in Rust (1.42.0) (judge verdict: Accepted)

struct Read<R: std::io::BufRead> {
    stdin: R,
    v: Vec<String>,
    i: usize,
}
impl<R:std::io::BufRead> Read<R> {
    pub fn new(stdin: R) -> Self {
        Read{
            stdin: stdin,
            v: Vec::new(),
            i: 0,
        }
    }
    pub fn read_line(&mut self) {
        self.i = 0; self.v.clear();
        let mut buf = String::new();
        self.stdin.read_line(&mut buf).unwrap();
        let buf = buf.trim().to_owned();
        let mut ws = buf.split_whitespace();
        loop {
            let x = ws.next();
            if x.is_none() {break;}
            let x = x.unwrap().to_owned();
            self.v.push(x);
        }
    }
    #[allow(dead_code)]
    pub fn read_t<T: std::str::FromStr>(&mut self) -> T {
        if self.i == self.v.len() {self.read_line();}
        let elem = &self.v[self.i];
        self.i += 1;
        elem.parse().unwrap_or_else(|_| panic!())
    }
    
    #[allow(dead_code)]
    pub fn read_i32(&mut self) -> i32 {
        if self.i == self.v.len() {self.read_line();}
        let elem = self.v[self.i].parse().unwrap();
        self.i += 1;
        elem
    }
    #[allow(dead_code)]
    pub fn read_usize(&mut self) -> usize {
        if self.i == self.v.len() {self.read_line();}
        let elem = self.v[self.i].parse().unwrap();
        self.i += 1;
        elem
    }
    #[allow(dead_code)]
    pub fn read_u64(&mut self) -> u64 {
        if self.i == self.v.len() {self.read_line();}
        let elem = self.v[self.i].parse().unwrap();
        self.i += 1;
        elem
    }
    #[allow(dead_code)]
    pub fn read_string(&mut self) -> String {
        if self.i == self.v.len() {self.read_line();}
        let elem = &self.v[self.i];
        self.i += 1;
        elem.to_owned()
    }
}

fn main() {
    use std::io;
    let stdin = io::stdin();
    let stdin = io::BufReader::new(stdin.lock());
    let read = Read::new(stdin);
    solve(read);
}

fn solve<R: std::io::BufRead>(mut r: Read<R>) {
    let a:i64 = r.read_t();
    let b:i64 = r.read_t();
    let n:i64 = r.read_t();
    
    let x = if b - 1 > n {
        n
    } else {
        b-1
    };
    let X = ((a*x) as f64 / b as f64) as i64;
    let Y = (x as f64 / b as f64) as i64;

    println!("{}",X-Y);
}