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

#define F(X) (printf("%lu\n",X))
#define I(X) (strtol(((char**)X)[1],0,10))
#define B(X) (main((X),0,0))
#define O _exit(1)

unsigned long main(
int           N,
unsigned long A,
unsigned long C
){
	return N<2?1:A?F(B(I(A)))*0:(A=B(N-1))+(C=B(N-2))+((A<C)&&(O,0));
}