#include using namespace std; #define rep(i,n) for(ll i=0;i<(n);++i) #define reps(i,n) for(ll i=1;i<=(n);++i) using ll = long long; using str = string; constexpr long long INF = (1LL<<60); constexpr long long MOD = (1e9+7); templateinline bool chmax(T &a,const T &b){if(ainline bool chmin(T &a,const T &b){if(a>b){a=b;return true;}return false;} inline void dump(){cout<inline void dump(Head&& head, Tail&&... tail){cout<(tail)...);} templateinline istream &operator>>(istream&input,vector&v){for(auto &elemnt:v)input>>elemnt;return input;} templatevector make_vector(size_t a){return vector(a);} templateauto make_vector(size_t a, Ts... ts){return vector(ts...))>(a, make_vector(ts...));} main(){ cin.tie(0); ios::sync_with_stdio(0); cout<>n>>s; map cnt; for(auto c:s)cnt[c]++; ll ans=0; ans += cnt['1']/2; ans += cnt['3']; ans += cnt['5']; ans += cnt['7']; cout<<(ans)<