#include<stdio.h>
#include<math.h>
int main()
{
    long long int a, b, n, max, diff;
    scanf("%lld%lld%lld", &a, &b, &n);
    if(n >= b)
    {
        diff = n - b;
        n = n - diff-1;
    }
    max = floor(a*n/b);
    printf("%lld\n", max);
}
