#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>
int main()
{
    long long int a,b,n;
    scanf("%lld %lld %lld",&a,&b,&n);
    if(b==n)
    {
        printf("%lld",(a*(n-1))/b-(a*((n-1)/b)));
    }
    else if(b>n)
    {
        printf("%lld",(a*n)/b-(a*(n/b)));
    }
    else
    {
        long long int range=((n/b)*b)+b-1;
        if(range>n)
        range=((n/b)-1)*b+b-1;
        printf("%lld",(a*range)/b-(a*(range/b)));
    }
}