#include <bits/stdc++.h>

using namespace std;

#define all(x) begin(x), end(x)

using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using vi = vector<int>;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);

    int n;
    string s;
    cin >> n >> s;

    int ans = 0;
    int ones = 0;
    for (char c : s) {
        if (c == '1') {
            ++ones;
        } else if (c == '9') {
        } else {
            ++ans;
        }
    }

    cout << ans + (ones / 2) << '\n';
    
    return 0;
}