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: Time Limit Exceeded)

use proconio::input;

fn main() {
    input! {
        a: f64,
        b: f64,
        n: u64,
    }

    let mut max = 0;
    let mut flag = false;

    for x in 0..(n + 1) {
        let left = ((a * (x as f64)) / b).floor() as u64;
        let right = (a as u64) * (((x as f64) / b).floor() as u64);
        let tmp = left - right;
        if tmp > 0 {
            flag = true;
        }
        if flag {
            if tmp == 0 {
                break;
            }
        }
        if max < tmp {
            max = tmp;
        }
    }

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