A. Andryusha and Socks

#include <bits/stdc++.h>

using namespace std ;
#define sz(s) int(s.size())
#define all(v) v.begin() , v.end()
#define imin INT_MIN
#define imax INT_MAX
typedef long long ll ;

void ABDEL3AL () {
    ios_base::sync_with_stdio(false); cin.tie(nullptr) , cout.tie(nullptr) ;
#ifndef ONLINE_JUDGE
    freopen("input.txt" , "r" , stdin) , freopen("output.txt" , "w" , stdout) ;
#endif
}


int main() {
    ABDEL3AL() ;
    int n , cnt = 0 , Max = imin ;
    cin >> n ;
    int arr[n] , freq[n + 1] = {0} ;
    for (int i = 0; i < n * 2; i++) {
        cin >> arr[i] , freq[arr[i]]++ ;
        cnt++ ;
        if (freq[arr[i]] == 2) cnt -= 2 ;
        Max = max (cnt , Max) ;
    }
    cout << Max ;

    return 0;
}