#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define EPS (1e-7)
#define INF (1e9)
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define all(x) x.begin(),x.end()
const double PI = acos(-1);
const ll MOD = 1000000007;
template<class T>
inline bool chmax(T &a, T b) {
    if(a < b) {
        a = b;
        return true;
    }
    return false;
}
 
template<class T>
inline bool chmin(T &a, T b) {
    if(a > b) {
        a = b;
        return true;
    }
    return false;
}
///////////////////////////////////////////////////////////////

int main() {
    ios::sync_with_stdio(false); cin.tie(nullptr);
	int N; cin >> N;
	string S; cin >> S;

	int count = 0;
	string T = "";
	rep(i,N) {
		if (S[i] == '1' || S[i] == '9') T += S[i];
		else count++;
	}
	int M = T.size();
	int cnt1 = 0;
	int cnt9 = 0;
	for (int i = M-1; i >= 0; i--) {
        if (T[i] == '9') cnt9++;
		else if (cnt9 > 0) {
			cnt9--;
            count++;
		} else {
			cnt1++;
		}
	}
	count += (cnt1/2);

	cout << count << endl;
}