#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int jePrastevilo(int u) {
	if (u <= 1)
		return 0;
	if (u == 2)
		return 1;
	for (int i = 2; i <= ceil(sqrt(u)); i++)
		if (u % i == 0)
			return 0;
	return 1;
}
int main (int argc, char ** argv) {
	if (argc != 1+1) {
		fprintf(stderr, "uporaba: %s <stevilo>\nprimer: %s 600851475143\n", argv[0], argv[0]);
		return 1;
	}
	unsigned long long p = 0;
	unsigned long long n = strtoll(argv[1], NULL, 10);
	unsigned long long i = 1;
	unsigned long long k = ceil(sqrt(n))+1;
	while (i < k) {
		i = i + 2;
		if (!jePrastevilo(i))
			continue;
		if (n % i == 0)
			p = i;
		if (1==1) {
			fprintf(stderr, "%lld, i = %lld, k = %lld, n = %lld\r", (i/k)*100, i,k,n);
		}
	}
	fprintf(stdout, "\rkonec. našel največje praštevilo %lld: %lld\n", n, p);
	return 0;
}