#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(ll i = 0, i##_len = (n); i < i##_len; i++)
#define reps(i, s, n) for(ll i = (s), i##_len = (n); i < i##_len; i++)
#define rrep(i, n) for(ll i = (n) - 1; i >= 0; i--)
#define rreps(i, e, n) for(ll i = (n) - 1; i >= (e); i--)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) ((ll)(x).size())
#define len(x) ((ll)(x).length())
#define endl "\n"
template<class T> void chmax(T &a, const T b){ a = max(a, b); }
template<class T> void chmin(T &a, const T b){ a = min(a, b); }

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    // ifstream in("input.txt");
    // cin.rdbuf(in.rdbuf());
    const ll inf = LONG_LONG_MIN / 2 - 1;
    ll n;
    cin >> n;
    string s;
    cin >> s;
    // 3, 5, 7は単品で使うのが良い
    string ns = "";
    rep(i, n) {
        if ((s[i] == '3') || (s[i] == '5') || (s[i] == '7')) continue;
        ns += s[i];
    }
    ll ans = n - len(ns);
    // 1と9を組み合わせて使う: 11, 19, 991
    n = len(ns);
    // dp[見た文字数][0:余り無し, 1:1余り, 2:9余り, 3:99余り] = 構成数
    vector<vector<ll>> dp(n + 1, vector<ll>(4, inf));
    dp[0][0] = 0;
    rep(i, n) {
        if (ns[i] == '1') {
            if (dp[i][0] != inf) chmax(dp[i + 1][1], dp[i][0]);
            if (dp[i][1] != inf) chmax(dp[i + 1][0], dp[i][1] + 1);
            if (dp[i][3] != inf) chmax(dp[i + 1][0], dp[i][3] + 1);
        }
        else {
            if (dp[i][0] != inf) chmax(dp[i + 1][2], dp[i][0]);
            if (dp[i][1] != inf) chmax(dp[i + 1][0], dp[i][1] + 1);
            if (dp[i][2] != inf) chmax(dp[i + 1][3], dp[i][2]);
        }
    }
    ll tmp = 0;
    rep(i, 4) chmax(tmp, dp[n][i]);
    ans += tmp;
    cout << ans << endl;
    return 0;
}