#include <iostream>
#include<vector>
#include<unordered_map>
using namespace std;
 
int main() {
	// your code goes here
	vector<int> a={1,3,4,5,2,7,8};
	unordered_map<int,int> m;
	int k=-7;
	for(int i=0;i<a.size();i++) {
		int sec=a[i]+k;
		if(m.find(sec)!=m.end()) {
			cout<<a[i]<<" "<<sec<<endl;
		}
		m[a[i]]=i;
	}
	return 0;
}