#include<stdio.h>

int main(void){
    long int A,B,N;
    scanf("%ld %ld %ld",&A,&B,&N);
    if(N<B){
        long int ans=(long int)N*A/B;
        printf("%ld\n",ans);
    }else{
        printf("%ld\n",A-1);
    }
    return 0;
}