using namespace std; using ll = long long; #define endl '\n' #define REP(i, x, y) for (decay<decltype(y)>::type i = (x), _##i = (y); i < _##i; ++i) #define PER(i, x, y) for (decay<decltype(x)>::type i = (x), _##i = (y); i > _##i; --i)
template<typename T=int> inline T read() { T x; cin >> x; return x; }
const int maxn = 2e5 + 500; int book[maxn], n; vector<int> a, b;
int main() { ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr); cin >> n; for (int i = 0; i < n; i++) { int t = read(); book[t] = 1; } for (int i = 1; i <= 2 * n; i++) { if (book[i] == 1) b.push_back(i); else a.push_back(i); } int p = 0, win = 0; for (int e: a) { int q = upper_bound(b.begin(), b.end(), e) - b.begin(); if (q > p) { ++win; p++; } } cout << win << endl; return 0; }