// Arup Guha
// 6/5/2026
// Solution to Kattis Problem: Code Cleanups
// https://open.kattis.com/problems/codecleanups

using namespace std;
#include <bits/stdc++.h>

int main() {

    // Read input.
    int n,x;
    cin >> n;
    vector<int> freq(370, 0);

    // Read days, store in frequency array.
    for (int i=0; i<n; i++) {
        cin >> x;
        freq[x] = 1;
    }

    int numClean = 0;
    int numD = 0, dirty = 0;

    for (int i=1; i<=367; i++) {

        // Update our dirty score.
        dirty += numD;

        // This is our count for tomorrow...
        if (dirty + numD + freq[i] >= 20) {
            dirty = 0;
            numClean++;
            numD = 0;
        }

        // We're good.
        else {
            numD += freq[i];
        }
    }

    // Last time.
    if (numD > 0) numClean++;

    // Ta da!
    cout << numClean << endl;

    return 0;
}