886C - Petya and Catacombs - CodeForces Solution

#include <bits/stdc++.h>
#define FOR_(i, s, n) for(int i = s; i < n; ++i)
#define FOR(i, n) FOR_(i, 0, n)
#define FORR(x, a) for(auto &x : a)
#define IN(x) FORR(y, x) cin >> y;
#define OUT(a) FORR(x, a) cout << x << " "; cout << "\n";
#define OUTM(m) FORR(x, m) cout << x.first << " " << x.second << "\n";
#define FAST ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define ALL(x) x.begin(), x.end()

using namespace std;
using ll = long long;
using ld = long double;

int main(){
    FAST
    int n, x;
    cin >> n;
    int ans = 1;
    set<int> was;
    was.insert(0);
    FOR(i, n){
        cin >> x;
        if (was.count(x)) was.erase(x);
        else ++ans;
        was.insert(i + 1);
    }
    cout << ans;
    return 0;
}