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

#define HASHSIZE 500009
int hash[HASHSIZE];

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

void check(int a){
	for(int h=a%HASHSIZE;hash[h];h+=1,h-=h<HASHSIZE?0:1){
		if(hash[h]==a){
			write(1,"2",1);
			_exit(0);
		}
	}
}

void insert(int a){
	int h;
	for(h=a%HASHSIZE;hash[h];h+=1,h-=h<HASHSIZE?0:1){
	}
	hash[h]=a;
}

main(){
	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);
}