#include <iostream>
#include <stdio.h>


int getPrevFib ( int curFib )
{
	int fib0 = 0;
	int fib1 = 1;
	while ( fib1 < curFib )
	{
		int fib01 =  fib0;
		fib0 = fib1;
		fib1 = fib0 + fib01;
	}
	return fib1;
}

int isFib ( int a )
{
	int fib1 = getPrevFib(a);
	int fib2 = getPrevFib(fib1);

	if ( fib1 + fib2 == a )
	{
		return 1;
	}
	else
	{
		return 0;
	}
}

int main ()
{
	printf("result: %d\n", isFib(21) );
	return isFib(21);
}