#include #define REP(i, n) for(int i = 0;i < n;i++) #define VSORT(v) sort(v.begin(), v.end()) #define VRSORT(v) sort(v.rbegin(), v.rend()) #define ll long long using namespace std; typedef pair P; typedef pair LP; typedef pair PP; typedef pair LPP; //typedef vectorvec; typedef vectorvec; typedef vector mat; typedef vector> Graph; const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1}; const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1}; const int INF = 1000000000; const ll LINF = 1000000000000000000;//1e18 const ll MOD = 1000000007; //const ll MOD = 998244353; const double PI = acos(-1.0); const double EPS = 1e-10; template inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; } template inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; } template inline void add(T &a, T b){a = ((a+b) % MOD + MOD) % MOD;}; int main(){ cin.tie(0); ios::sync_with_stdio(false); int n; cin >> n; string S; cin >> S; map mp; ll ans = 0; REP(i,n){ int m = S[i] - '0'; mp[m]++; if(m == 9 && mp[1] > 0){ ans++; mp[9]--, mp[1]--; } } ans += mp[1] / 2; ans += mp[3] + mp[5] + mp[7]; cout << ans << endl; }