Cetiri Solution:

#include <bits/stdc++.h>
using namespace std;

int main(){
    // #ifndef TESTING
    // freopen("input.txt", "r", stdin);
    // freopen("output.txt", "w", stdout);
    // #endif

    int nums[3];
    for(auto &i: nums){
        cin >> i;
    }
    sort(nums, nums+3);
    int diff1 = nums[1] - nums[0];
    int diff2 = nums[2] - nums[1];
    if(diff1 == diff2){
        cout << nums[2] + diff1;
    } else if(diff1 > diff2){
        cout << nums[0] + diff2;
    } else {
        cout << nums[1] + diff1;
    }

    return 0;
}