#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());
	int n=v.size();
	if(n&1)
	{
		cout<<v[n/2];
	}
	else
	{
		cout<<(v[n/2-1]+v[n/2])/2.0;
	}
	return 0;
}