#include<iostream>
#include<string>
#include<cstring>
#include<algorithm>
#include<vector>
#include<iomanip>
#include<math.h>
#include<complex>
#include<queue>
#include<deque>
#include<stack>
#include<map>
#include<set>
#include<bitset>
#include<functional>
#include<assert.h>
#include<numeric>
using namespace std;
#define REP(i,m,n) for(int i=(int)(m) ; i < (int) (n) ; ++i )
#define rep(i,n) REP(i,0,n)
using ll = long long;
const int inf=1e9+7;
const ll longinf=1LL<<60 ;
const ll mod=1e9+7 ;
#define PI 3.141592653589793


int main(){
  int N; cin >> N; string S; cin >> S; int ans = 0, one = 0, nine = 0;
  rep(i, N){
    if(S[i]!='1' && S[i]!='9') ans++;
    if(S[i]=='1') one++;
    if(S[i]=='9'){
      if(one>0){
        one--; ans++;
      }
    }
  }
  if(one>0) ans+=one/2;
  cout <<ans <<endl;
}