#include<stdio.h>
#include<math.h>

int main(void){
    int A,B,N;
    scanf("%d %d %d",&A,&B,&N);
    int tmp;
    int i;
    int max=floor(A/B)-A*floor(1/B);
    for(i=1; i<=N; i++){
        tmp = floor(A*i/B) - A*floor(i/B);
        if(tmp > max)
            max = tmp;
    }
    printf("%d\n",tmp);
    return 0;
}