#include <stdio.h>
int K, L, i;
int main()
{
  scanf("%d", &K);
  for (L=2; L<K; L++)
   for (i=1; i<L; i++)
   if ((K-L-1)%(L+i)==0) goto stop;
stop: printf("%d", L);
  return 0;
}

Sorry my bad english.
1) You solve is "ploho_chitaetsya))"
2) You solve is very long.
The AC solve run for O(n^(1/2)), or O(sqrt(n)).