#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
#include<unordered_map>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int, int>pi;
typedef pair<ll, ll>pl;
typedef vector<pi>vpi;
typedef vector<pl>vpl;
typedef vector<vi> vvi;
typedef vector<vl> vvl;
typedef vector<string> vs;
typedef vector<bool> vb;
const long double PI = acos(-1);
const ll oo = 1e18;
const int MOD = 1e9 + 7;
const int N = 2e5 + 7;
#define endl '\n'
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define read(v) for (auto& it : v) scanf("%d", &it);
#define readL(v) for (auto& it : v) scanf("%lld", &it);
#define print(v) for (auto it : v) printf("%d ", it); puts("");
#define printL(v) for (auto it : v) printf("%lld ", it); puts("");
void solve() {
int n;
cin >> n;
vi v(n);
for (auto& it : v)
cin >> it;
int ans = 0;
vb vis(n, false);
for (int i = 0; i < n; i++) {
if (vis[i])
continue;
int h = v[i] - 1;
for (int j = 0; j < n; j++)
if (j != i && !vis[j] && v[j] == h)
h--, vis[j] = true, j = 0;
vis[i] = true, ans++;
}
cout << ans << endl;
}
int t = 1;
int main() {
//#ifndef ONLINE_JUDGE
// freopen("input.txt", "r", stdin);
//#endif
//scanf("%d", &t);
while (t--) solve();
}
