#pragma GCC optimize("Ofast")
#pragma GCC target("avx2")

#define HASHSIZE 500009
int hash[HASHSIZE];
int hk1,hk2;

char*mmap();
#define RD(v) int v=0;{int _c;while(_c=*rp++-48,_c>=0)v=v*10+_c;}

void check(int a){
	int h=(long)a*hk1%HASHSIZE;
	if(hash[h]==a){
		write(1,"2",1);
		_exit(0);
	}
	if(hash[h]){
		int h2=(long)(a/HASHSIZE+1)*hk2%HASHSIZE;
		do{
			h+=h2;
			h-=h<HASHSIZE?0:HASHSIZE;
			if(hash[h]==a){
				write(1,"2",1);
				_exit(0);
			}
		}while(hash[h]);
	}
}

void insert(int a){
	int h=(long)a*hk1%HASHSIZE;
	if(hash[h]){
		int h2=(long)(a/HASHSIZE+1)*hk2%HASHSIZE;
		do{
			h+=h2;
			h-=h<HASHSIZE?0:HASHSIZE;
		}while(hash[h]);
	}
	hash[h]=a;
}

main(){
	unsigned t=time(0);
	hk1=t%HASHSIZE?:1;
	hk2=t/HASHSIZE?:1;

	char*rp=mmap(0l,11*100001,1,2,0,0ll);
	while(*rp++!=10);
	do{
		RD(a);
		check(a);
		check(a+2);
		insert(a+1);
	}while(*rp);
	write(1,"1",1);
	_exit(0);
}