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

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

    int x = 0, max = 0, result;

    while(1)
    {
        result = (int)(floor(a*x/b) - (a*floor(x/b)));

        if(result >= max)
            max = result;

        x++;

        if(x > n)
            break;
    }

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

    return 0;
}
