#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main()
{
    long long int a, b, n;
    scanf("%lld%lld%lld", &a, &b, &n);

    int x, max = 0, result;

    for(x = 0; x <= n; x++)
    {
        result = (floor(a*x*1.0/b) - (a*floor(x*1.0/b)));

        if(result >= max)
            max = result;
    }

    printf("%d\n", max);

    return 0;
}
