#include <stdio.h>
#include <stdlib.h>
int main(){
  long int A,B,N,max,y,s,i;
  scanf("%ld %ld %ld",&A,&B,&N);
  if(N>=B) y=B-1;
  else y=N;
  s=y/B;
  max=A*y/B-A*s;
  printf("%ld",max);
  return 0;
}