#include<stdio.h>

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