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 JavaScript (Node.js 12.16.1) (judge verdict: Wrong Answer)

function Main(input){
  input = input.split(' ').map(x=>BigInt(x));
  var a = input[0];
  var b = input[1];
  var n = input[2];
  if (b==1){
    var max = a*n 
  }else if (n<b){
    var max = a*n/b - a*(n/b);
  }else{
    var border = (n+1n)/b;
    var t = 1n;
    var max = 0n;
    for (let t = 1n;t<=border;t++){
      var now = a*(b*t-1n)/b - a*((b*t-1n)/b);
      if (now > max){
        max = now;
      }
    }
  }
  console.log(max.toString())
}
  

Main(require("fs").readFileSync("/dev/stdin", "utf8"));