#include <stdio.h>
#include <string.h>

int main()
{
    long long a, b, n, x, max = 0;
    scanf("%lld %lld %lld", &a, &b, &n);

    x = n / b;

    long long ret = (a * x) / b - a * (x / b);
    max = max > ret ? max : ret;
    x += b;

    max = max > ((a * n) / b - a * (n / b)) ? max : ((a * n) / b - a * (n / b));

    printf("%d", max);

    return 0;
}