sleep() in C

So, I've been trying to use the sleep function in C, but I have a problem. If I use it once, like, for example:

printf("First Line.\n");
sleep(5);
printf("Second Line.");
Then it works just fine. But if I try doing that same thing, so:

printf("First Line.\n");
sleep(5);
printf("Second Line.\n");
sleep(5);
printf("Third Line.");
It just waits 10 seconds then displays the next two lines at once. Is there some work around for this?

be sure to fflush(stdin); too, lel