#include<bits/stdc++.h>
using namespace std;
int main()
{
	vector<int> v;
	int x;
	while(cin>>x,x)
	{
		v.push_back(x);
	} 
	sort(v.begin(),v.end());
	if(v.size()%2!=0)
	{
		cout<<v[v.size()/2];
	}
	else
	{
		cout<<(v[v.size()/2]+v[v.size()/2-1])/2.0<<endl;
	}
	return 0;
}