#include<stdio.h>

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