A prime calculator to test the speed of a server

primes.c

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

/**
 * Defined as a default. You can pass any value as first parameter.
 */
#define LIMIT (200000)

/*
 * This software is not useful to calculate the prime numbers
 * but really a good method to test the speed of a CPU. Note
 * the program should work on a single core and this could
 * modify the speed perception.
 *
 * How to use it?
 * cc primes.c && time ./a.out
 *
 * This will give you the CPU usage used by the software. It
 * is a very fast and very simple way to check the speed of
 * a VPS (like Amazon EC2 or any other provider).
 */

int isPrime(int input){
        for(int i = 2; i < input - 1; i++){
                if( input % i == 0) return false;
        }
        return true;
}

int main(int argc, char **argv) {
        time_t rawtime;
        int limit = LIMIT;
        if(argc > 1){
                limit = atoi(argv[1]);
        }

        time_t previous = time(&rawtime);
        int last = 2;
        for (int i = 2; i < limit; i++) {
                if(isPrime(i)){
                        last = i;
                        time(&rawtime);
                        if(rawtime > previous){
                                printf("%d...\n", last);
                                previous++;
                        }
                }
        }
        printf("%d (done)\n", last);
        return 0;
}