/*
	LRS(Language Recognition System)

	±³Àç 241ÂÊ <¿¹Á¦9>¿¡ ´ëÇÑ ¾ð¾îÀÎ½Ä ÇÁ·Î±×·¥

	Å×½ºÆ® ½ºÆ®¸µ : "abb$", "aaabbb$"
*/
/*
	Language Recognizer for the following CFG.

	G = ({S, A}, {a, b}, P, S)
		P: S --> aAb
		   A --> aS
		   A --> b
*/

#include <stdio.h>

char ch;
int errflag = 0;

/*
	Recognition-failed message.
*/
void error()
{
	if (!errflag) {
		puts("FAIL");
		errflag = 1;
	}
}

void pa()
{
	if (ch == 'a')
		ch = getchar();
	else error();
}

void pb()
{
	if (ch == 'b')
		ch = getchar();
	else error();
}

/*
	S --> aAb
*/
void pS()
{
	void pA();

	if (ch == 'a') {
		pa(); pA(); pb();
	} else error();
}

/*
	A --> aS
	A --> b
*/
void pA()
{
	switch (ch) {
	case 'a':
		pa(); pS();
		break;
	case 'b':
		pb();
		break;
	default:
		error();
	}
}

void main()
{
	ch = getchar();
	pS();
	if (!errflag && ch == '$') puts("OK");
	else error();
}