#include<iostream>
using namespace std;
int main(){
	int a,b,c,d,i=1000;
	for(i=1000;i<9999;i++){
		a=i/1000;
		b=i/100%10;
		c=i/10%10;
		d=i%10;
		if(a==b&&c==d){
			cout<<i<<endl;
		}
	}
}
/**************************************************************
	Problem: 1092
	User: panyuchen
	Language: C++
	Result: Wrong Answer
****************************************************************/