
#include <stdio.h>

int main()
{
    long long int a, b, n, x, max = -10000,c;
    scanf("%lld%lld%lld", &a, &b, &n);

    for (x = 1; x <= n; x++)
    {
        c = ((a * x) / b) - (a * (x / b));
        if (c >= max)
        {
            max = c;
        }
    }
    printf("%lld\n", max);
    return 0;
}