#include <stdio.h>
#include <stdbool.h>
#include <inttypes.h>
#include <math.h>
bool is_prime(uint64_t n) {
if (n <= 1) return false;
if (n <= 3) return true;
if ((n % 2 == 0) || (n % 3 == 0)) return false;
uint64_t sqrt_n = sqrt(n);
for (uint64_t i = 5; i <= sqrt_n; i += 6) {
if ((n % i == 0) || (n % (i + 2) == 0)) {
return false;
}
}
return true;
}
int main(int argc, char **argv) {
if (argc < 2) {
fputs("Pass a positive integer as an argument.\n", stderr);
return 1;
}
uint64_t input;
if ((argv[1][0] == '-') || (sscanf(argv[1], "%" SCNu64, &input) != 1)) {
fputs("This is not a positive integer.\n", stderr);
return 1;
}
printf("This integer %s prime.\n", is_prime(input) ? "is" : "is not");
return 0;
}