#include<stdio.h>

int main(void){
    long long int A,B,N,x,n=0,temp;

    scanf("%lld %lld %lld",&A,&B,&N);

    if(A>B){
    /*for(x=0;x<=N;x++){
        if(x==B-1){
        temp = A*x/B - x/B*A;
        printf("%lld\n",temp);
        }
    }*/
    x=B-1;
    temp = A*x/B - x/B*A;
    printf("%lld",temp);
    }


    if(A<=B) printf("%lld",A*N/B - N/B*A);
    

    return 0;
}