#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) begin(v),end(v)
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
using ll = long long;
using pii = pair<int, int>;
constexpr ll INF = 1ll<<30;
constexpr ll longINF = 1ll<<60;
constexpr ll MOD = 1000000007;
constexpr bool debug = false;
//---------------------------------//

int main() {
	int N;
	cin >> N;
	string S;
	cin >> S;
	// 11, 19, 991
	int other = 0, one = 0, nine = 0;
	vector<int> v;
	for (char c : S) {
		const int n = c - '0';
		if (n == 3 || n == 5 || n == 7) ++other;
		else {
			v.emplace_back(n);
			one += n == 1;
			nine += n == 9;
		}
	}
	
	int ans = other;
	int state = 0, cur = 0;
	REP(i, v.size()) {
		if (state <= 1 && v[i] == 9) {
			--nine;
			++state;
		}
		else if (state == 2 && v[i] == 1) {
			--one;
			state = 0;
			++cur;
			const int c = min(one, nine);
			chmax(ans, other + cur + c + (one - c) / 2);
		}
	}
	cout << ans << endl;
}