#include <iostream>
#include <algorithm>
#include <bitset>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <cstring>
#include <utility>
#include <vector>
#include <complex>
#include <valarray>
#include <fstream>
#include <cassert>
#include <cmath>
#include <functional>
#include <iomanip>
#include <numeric>
#include <climits>
#include <random>

#define _overload(a, b, c, d, ...) d
#define _rep1(X, A, Y) for (int (X) = (A);(X) <= (Y);++(X))
#define _rep2(X, Y) for (int (X) = 0;(X) < (Y);++(X))
#define rep(...) _overload(__VA_ARGS__, _rep1, _rep2)(__VA_ARGS__)
#define rrep(X,Y) for (int (X) = Y-1;(X) >= 0;--(X))
#define all(X) (X).begin(),(X).end()
#define len(X) ((int)(X).size())
#define mod(n, m) (((n)%(m)+(m))%m)
#define fi first
#define sc second
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> Pii;
typedef pair<ll,ll> Pll;
const int INFINT = 1 << 30;                          // 1.07x10^ 9
const ll INFLL = 1LL << 60;                          // 1.15x10^18
const double EPS = 1e-10;
const int MOD = 1000000007;
const int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};

const int MAX_N = 200000;
int N;
string S;

int main() {
    cin >> N;
    cin >> S;

    int ans = 0;
    string extracted;
    for (int i = 0; i < N; ++i) {
        if (S[i] == '1' || S[i] == '9') {
            extracted += S[i];
        } else {
            ++ans;
        }
    }

    int one = 0;
    for (int i = 0; i < len(extracted); ++i) {
        if (extracted[i] == '1') ++one;
        else {
           if (one > 0)  {
               ++ans; --one;
           }
        }
    }

    ans += one/2;

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