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 C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <math.h>
int main()
{
    long long int a,b,n;
    scanf("%lli %lli %lli",&a,&b,&n);
    int i;
    long long int c;
    long long int d;
    long long int result;
    for(i=1; i<sqrt(n)+sqrt(b)+sqrt(a); i++)
    {
        c=(a*n)/b;
        d=n/b;
        d=d*a;
        c=c-d;
        if(i==0||c>result)
        {
            result=c;
        }
        c=(a*i)/b;
        d=i/b;
        d=d*a;
        c=c-d;
        if(c>result)
            result=c;
        n--;
    }
    printf("%lli",result);
    return 0;
}