#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdbool.h>
#define erreur(message) { fprintf(stderr,message) ; exit(EXIT_FAILURE); }
int premier(int n){
int taille=n*n+1;
int result=-1;
  int *crible = malloc( taille * sizeof(int) );
int i;
for(i=0;i<=n*n;i++) crible[i]=true;
for(i=2;i<=n;i++)
  if(crible[i]){
    int j=i*i;
    while(j<=n*n){ crible[j]=false; j += i; }
    }
for(i=n*n;i>=0;i--) if(crible[i]){ result=i; break; }
return result;
}

int main(void){
int n;									
if(scanf("%d",&n)!=1) erreur("Echec de lecture du nombre\n");
printf("premier -> %d\n",premier(n));
return 0;
}