#include <bits/stdc++.h>
#define _overload3(_1, _2, _3, name, ...) name
#define _rep(i, n) repi(i, 0, n)
#define repi(i, a, b) for (ll i = (ll)(a); i < (ll)(b); ++i)
#define rep(...) _overload3(__VA_ARGS__, repi, _rep, )(__VA_ARGS__)
#define ll long long
#define lld long double
#define ALL(x) x.begin(), x.end()
#ifdef DEBUG
#define line() cerr << "[" << __LINE__ << "] ";
#define dump(i) cerr << #i ": " << i << " ";
#define dumpl(i) cerr << #i ": " << i << endl;
#else
#define line(i)
#define dump(i)
#define dumpl(i)
#endif
using namespace std;
int main(int argc, char const *argv[])
{

    string s;
    int tmp;
    cin >> tmp >> s;
    string rest = "";
    int ans = 0;
    rep(i, s.size())
    {
        if (s[i] != '1' && s[i] != '9') //ひと桁の素数なら
        {
            ans++;
        }
        else
        {
            rest += s[i];
        }
    }
    s = rest;
    rest = "";
    int front = 0;
    int rear = s.size() - 1;
    while (front < rear)
    {
        if (s[front] == '1' && s[rear] == '9')
        {
            ans++;
            front++;
            rear--;
        }
        else
        {
            if (s[front] != '1')
            {
                rest = "9" + rest;
                front++;
            }
            if (s[rear] != '9')
            {
                rest = rest + "1";
                rear--;
            }
        }
    }
    //cerr << rest << endl;
    s = rest;
    rest = "";
    rep(i, s.size())
    {
        if (s[i] == '1' && i != s.size() - 1 && s[i + 1] == '1')
        {
            ans++;
            i++;
        }
        else
        {
            rest += s[i];
        }
    }
    //cerr << rest << endl;
    s = rest;
    rep(i, s.size() - 2)
    {
        if (s[i] == '9' && s[i + 1] == '9' && s[i + 2] == '1')
        {
            ans++;
            //break;
        }
    }
    //cerr << rest << endl;

    cout << ans << endl;
    return 0;
}