#include #define rep(i, n) for(int(i) = 0; (i) < (n); (i)++) #define FOR(i, m, n) for(int(i) = (m); (i) < (n); (i)++) #define ALL(v) (v).begin(), (v).end() #define LLA(v) (v).rbegin(), (v).rend() #define PB push_back #define MP(a, b) make_pair((a), (b)) using namespace std; template inline vector make_vec(size_t a, T val) { return vector(a, val); } template inline auto make_vec(size_t a, Ts... ts) { return vector(a, make_vec(ts...)); } template inline T read() { T t; cin >> t; return t; } template inline vector readv(size_t sz) { vector ret(sz); rep(i, sz) cin >> ret[i]; return ret; } template inline tuple reads() { return {read()...}; } template struct edge { int to; T cost; edge(int t, T c) : to(t), cost(c) {} }; using ll = long long; using pii = pair; using pll = pair; using Graph = vector>; template using WGraph = vector>>; const int INF = 1 << 30; const ll LINF = 1LL << 60; const int MOD = 1e9 + 7; int main() { ios::sync_with_stdio(false); cin.tie(nullptr); int N = read(); string s = read(); string t = ""; int res = 0; rep(i, N) { if(s[i] == '1' || s[i] == '9') { t += s[i]; } else { res++; } } stack st; rep(i, t.size()) { if(t[i] == '9' && !st.empty() && st.top() == '1') { st.pop(); res++; } else { st.push(t[i]); } } int cnt1 = 0, cnt9 = 0; while(!st.empty()) { if(st.top() == '1') cnt1++; else cnt9++; st.pop(); } cout << res + max(cnt1 / 2, min(cnt1, cnt9 / 2)) << endl; }