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

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int N;
    cin >> N;
    vector<int> tb(100002);
    for(int i = 0, v; i < N; i++){
        cin >> v;
        tb[v]++;
    }
    auto f = [&](int v){
        if(N < v * 2)return false;
        int cnt = 0;
        for(int i = 0; i < v; i++){
            cnt += max(0, 2 - tb[i]);
        }
        return (cnt <= 1);
    };
    int ok = 0, ng = 100002, mid;
    while(ok + 1 < ng){
        mid = (ok + ng) / 2;
        if(f(mid))ok = mid;
        else ng = mid;
    }
    cout << ok << '\n';
}