#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005

int main() {
    int n;
    cin >> n;
    string s; cin >> s;

    int ans = 0;

    string t;
    rep(i,n){
        if(s[i] == '1' || s[i] == '9'){
            t += s[i];
        }else{
            ans++;
        }
    }
    int m = t.size();
    int one = 0;
    int nine = 0;
    rep(i,m){
        if(t[i] == '1'){
            one++;
        }else{
            if(one == 0){
                nine++;
            }else{
                one--;
                ans++;
            }
        }
    }

    nine = nine / 2;
    ans += min(nine, one);
    one -= min(nine, one);
    ans += one / 2;

    cout << ans << endl;
    return 0;
}