#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int main()
{     long long int n,a=0;     cin>>n;     if(n==2)     cout<<2;     if(n==3)     cout<<3;     if(n==4)     cout<<3;     if((n%2==0)&&(n!=2))     n=n-1;     for(int i=n;i>=3&&a==0;i=i-2)//µ±Ç°Êý×Ö      {         for(int j=3;j<=(i+1)/2&&a==0;j++)//¼ì²éÊÇ·ñÓÐÒòÊý          {             if(i%j==0)    //ÊǺÏÊý              break;             else        //ÊÇÖÊÊý              {                 if(j==(i+1)/2)                 {                     a=1;                     cout<<i;                     break;                 }             }          }     }     return 0;
}