#include <bits/stdc++.h>
#include <unordered_map>
#include <unordered_set>
#define endl '\n'
#define fast ios::sync_with_stdio(0), cin.tie(0)
#define debug cout << "ok" << endl
#define finish(x) return cout << x << endl, 0
typedef long long ll;
typedef long double ldb;
const int md = 1e9 + 7, inf = 1e9 + 7;
const ll hs = 199;
const ldb eps = 1e-9, pi = acos(-1);
using namespace std;
int n, x, a[1000005] = {}, ans = 0;
int main() {
fast;
cin >> n;
while (n--) {
cin >> x;
if (a[x]) {
a[x]--;
a[x - 1]++;
}
else {
a[x - 1]++;
ans++;
}
}
finish(ans);
}
