//#pragma GCC optimize ("-O3","unroll-loops")
#include<iostream>
#include<string>
#include<algorithm>
#include<vector>
#include<queue>
#include<map>
#include<math.h>
#include<iomanip>
#include<set>
#include<numeric>
#include<cstring>
#include<cstdio>
#include<functional>
#include<bitset>
#include<limits.h>
#include<cassert>
#include<iterator>
#include<complex>
#include<stack>
#include<unordered_map>
#include<unordered_set>
#include<time.h>
#include <random>

using namespace std;

#define REP(i, n) for(int i = 0;i < n;i++)
#define REPR(i, n) for(int i = n;i >= 0;i--)
#define FOR(i, m, n) for(int i = m;i < n;i++)
#define FORR(i, m, n) for(int i = m;i >= n;i--)
#define SORT(v, n) sort(v, v+n);
#define VSORT(v) sort(v.begin(), v.end());
#define REVERSE(v,n) reverse(v,v+n);
#define VREVERSE(v) reverse(v.begin(), v.end());
#define ll long long
#define pb(a) push_back(a)
#define print(x) cout<<x<<'\n';
#define pe(x) cout<<x<<" ";
#define lb(v,n) lower_bound(v.begin(), v.end(), n);
#define ub(v,n) upper_bound(v.begin(), v.end(), n);
#define int long long
#define all(x) (x).begin(), (x).end()
#define print_space(v) REP(i,v.size())cout << v[i] << ((i == v.size() - 1) ? "\n" : " ");
//#define double long double

template<typename T1, typename T2> inline void chmin(T1 & a, T2 b) { if (a > b) a = b; }
template<typename T1, typename T2> inline void chmax(T1& a, T2 b) { if (a < b) a = b; }
typedef pair<int, int>P;
const int MOD = 1e9 + 7;
const int MAX = 200060;
const double pi = acos(-1);
const ll INF = 1e18;



bool used[200020];
void solve() {
	ll ans = 0;
	string S;
	int N; cin >> N >> S;
	int l = 0, r = 1;
	while (l < N&&r < N) {
		while (S[l] != '1') {
			l++;
			if (l >= N)break;
		}
		if(r<=l)r = l + 1;
		if (r >= N)break;
		while (S[r] != '9') {
			r++;
			if (r >= N)break;
		}
		if (r >= N)break;
		used[l] = true;
		used[r] = true;
		if (r < N)ans++;
		l++, r++;
	}
	string T;
	int nine = 0, one = 0;
	REP(i, N) {
		if (used[i])continue;
		if (S[i] == '3' || S[i] == '5' || S[i] == '7') {
			ans++;
		}
		else if (S[i] == '1') {
			if (nine >= 2) {
				nine -= 2;
				ans++;
			}
			else one++;
		}
		else if (S[i] == '9') {
			nine++;
		}
	}
	ans += one / 2;
	print(ans);
}


signed main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	solve();
}