//#pragma GCC optimize("O3")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,tune=native")
//#pragma GCC optimize ("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int n;
cin >> n;
vector<int> h(n);
for (int i = 0; i < n; i++) {
cin >> h[i];
}
unordered_map<int, int> a;
int ans = 0;
for (int i = 0; i < n; i++) {
if (a[h[i]]) {
a[h[i]]--;
} else {
ans++;
}
a[h[i] - 1]++;
}
cout << ans;
return 0;
}
