#include <iostream>
using namespace std;

int main(){
    int N;
    string S,T = "";
    cin >> N >> S;
    int ans = 0;
    for(int i=0;i<N;i++){
        if(S[i]!='1' && S[i]!='9') ans++;
        else T += S[i];       
    }
    int one = 0,nine = 0;
    int ans2 = 0;
    int n = T.size();
    for(int i=n-1;i>=0;i--){
        if(T[i]=='9') nine++;
        else{
            if(nine){
                nine--;
                ans2++;
            }else one++;
        }
    }
    ans2 += one/2;
    one = 0,nine = 0;
    int ans3 = 0;
    for(int i=0;i<N;i++){
        if(T[i]=='9') nine++;
        else{
            if(nine>=2){
                nine -= 2;
                ans3++;
            }else one++;
        }
    }
    ans3 += one/2;
    cout << ans+max(ans2,ans3) << endl;
}