tailfibonacci.c

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

uint64_t tailfibonacci(uint64_t n, uint64_t prev, uint64_t cur, uint64_t sum)
{
	if (n == 0) return sum;
	return tailfibonacci(n-1, cur, sum, sum+cur);
}

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

	printf("Fibonacci(%" PRIu64 ") = %" PRIu64 "\n", n, tailfibonacci(n, 1, 1, 0));

	return EXIT_SUCCESS;
}