#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <cstring>
#include <string>
#include <algorithm>
#include <cmath>
#include <vector>
#include <queue>
#include <stack>
#include <deque>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>

using namespace std;
#define INF 1234567890

int main() {
	ios::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);

	int arr[3];
	cin >> arr[0] >> arr[1] >> arr[2];
	sort(arr, arr + 3);
	
	if (arr[1] - arr[0] == arr[2] - arr[1])
		cout << arr[2] + arr[2] - arr[1];
	else if(arr[1] - arr[0] < arr[2] - arr[1])
		cout << (arr[2] + arr[1]) / 2;
	else
		cout << (arr[1] + arr[0])/2;
	

	return 0;
}