#include <bits/stdc++.h>
using namespace std;
const int maxn = (int)1e6+5;
int n;
int a[maxn];
namespace sub1 {
int ans = 0;
int vis[5005];
bool check () {
return (n <= 5000);
}
void solve () {
for (int i = 1;i <= n; i++) {
bool found = 0;
for (int j = 1;j < i; j++) {
if (a[i]+1 == a[j] && !vis[j]) {
found = 1;
vis[j] = 1;
}
}
ans += (1^found);
}
cout << ans << "\n";
}
}
namespace sub2 {
int ans = 0;
int cnt[maxn];
void solve () {
for (int i = 1;i <= n; i++) {
if (cnt[a[i]+1] > 0) {
cnt[a[i]+1]--;
}
else {
ans++;
}
cnt[a[i]]++;
}
cout << ans << "\n";
}
}
void read_and_prep() {
cin >> n;
for (int i = 1;i <= n; i++) cin >> a[i];
}
int main () {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
read_and_prep();
sub2::solve();
return 0;
// if (sub1::check()) sub1::solve();
// else sub2::solve();
return 0;
}
