/*
 * compute elements of the Fibonacci sequence using a loop
 * (more efficient than recursive version, but also more complicated)
 */
#include <stdio.h>

long fib(long n) {
	if (n <= 1) {
		return 1;
	}
	long minus2 = 1;
	long minus1 = 1;
	long current; 
	for (long index = 2; index <= n; ++index) {
		current = minus2 + minus1;
		minus2 = minus1;
		minus1 = current;
	}
	return current;
}

int main(void) {
	long n;
	printf("enter index of the element you want\n");
	if (scanf("%ld", &n) == 1) {
		printf("element %ld is %ld\n", n, fib(n));
	}
	else {
		printf("not number\n");
		return 1;
	}
	return 0;
}