#include<stdio.h>
#include<stdlib.h>

int main (void){
  
  int A;
  long B,N;
  scanf("%d%ld%ld",&A,&B,&N);
  
  int a=0,b;
  int c,d;
  for(long x=1;x<=N;x++){
    c = A*x/B;
    d = x/B;
    b = c - A*d ;
    if (a <= b) a = b;
  }
  
  printf("%d",a);
  
  return 0;
}