/*
 * FileName:     D_fix
 * CreatedDate:  2020-05-02 22:31:53 +0900
 * LastModified: 2020-05-02 22:41:29 +0900
 */

#include <stdio.h>

int main(void){
    long long int a,b,n;
    scanf("%lld %lld %lld",&a,&b,&n);
    long long int nn=(a*n-a*n%b)/b-a*(n-n%b)/b;
    long long int nn_=(a*(n-1)-a*(n-1)%b)/b-a*(n-1-(n-1)%b)/b;
    if(nn>=nn_){
        printf("%lld\n",nn);
    }
    else{
        printf("%lld\n",nn_);
    }
}
