# include <bits/stdc++.h>

using namespace std;

typedef long long ll;

set < ll > s;
ll q;

main(){
    freopen("exam.in", "r", stdin);
    freopen("exam.out", "w", stdout);
    for(ll i = 1; i <= (ll)3e5; ++i) s.insert(i);
    scanf("%lld", &q);
    while(q--){
        ll x;
        scanf("%lld", &x);
        if(x > 0){
            printf("%lld\n", *s.lower_bound(x));
            s.erase(s.lower_bound(x));
        }
        else{
            s.insert(-x);
        }
    }
    return 0;
}