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

int main(void)
{
    long a,b,n=0;
    int ans_all = 0;
//    int ans1,ans2,ans_all = 0;
    int max_ans = 0;
    int i=0;


    scanf("%ld %ld %ld",&a,&b,&n);

    for(i=1; i<= n; i++)
    {
        if(i < b){
            ans_all = (a * i) / b ;
        }else{
           ans_all = ((a * i) / b ) -(a * (i/b)); 
        }

        if(max_ans < ans_all)
        {
            max_ans = ans_all;
        }
    }

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

    return 0;
}