#include <bits/stdc++.h>
#define pb push_back
#define eb emplace_back
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define uniq(x) x.erase(unique(all(x)), x.end())
#define rall(x) x.rbegin(), x.rend()
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int mod = 1e9 + 7;
const int LOG = 20;
const int maxn = 1e6 + 5;
void setIO() {
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
}
int occ[maxn];
int32_t main() {
setIO();
int n, x;
cin >> n;
int ans = 0;
for(int i=0; i<n; i++) {
cin >> x;
occ[x]++;
if(occ[x+1] > 0) occ[x+1]--;
else ans++;
}
cout << ans << '\n';
return 0;
}
