recfibonacci.c

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

uint64_t fibonacci(uint64_t n)
{
	if (n == 2 || n == 1) return 1;
	return fibonacci(n-1) + fibonacci(n-2);
}

int main(int argc, char** argv)
{
	uint64_t n = strtoull(argv[1], NULL, 0);

	printf("Fibonacci(%" PRIu64 ") = %" PRIu64 "\n", n, fibonacci(n));

	return EXIT_SUCCESS;
}