#include <stdio.h>

int main(){
        long x = 0, i = 0, j = 0;
        scanf ("%i", &x);
        if (x<0) x = -x;
        short array_all_numbers[x+1];
        for (i = 0; i<x+1; i++){
                array_all_numbers[i] = 0;
        }
        for (i = 2; i < x+1; i++) {
                if (array_all_numbers[i] == 0) {
                        for (j = i * i; j < x+1; j+=i) {
                                array_all_numbers[j] = 1;
                        }
                }
        }
        for (i = x; i > 1; i--){
                if ((array_all_numbers[i]==0) && ((x%i) == 0)){
                printf("%ld", i);
                break;
                }
        }
	return 0;
}