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

int main()
{
    int i, j;
    int value;
    int *number_list;
    int largest_prime_factor;
    
    printf("Please enter an Integer\n");
    scanf("%d", &value);
    
    number_list = (int *)malloc((value + 1) * sizeof(int));
    
    for(i = 0; i <= value; i++)
        number_list[i] = 0;

    for(i = 2; i <= value; i++)
        if(number_list[i] != 1)
            for(j = 2; (i * j) <= value; j++)
                number_list[(i * j)] = 1;
    
    for(i = 2; i <= value; i++)
        if(number_list[i] == 0 && value % i == 0)
            largest_prime_factor = i;

    printf("%d", largest_prime_factor);
}