//include
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <unordered_map>
#include <climits>
#include <set>
#include <unordered_set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <queue>
#include <random>
#include <complex>
#include <regex>
#include <locale>
#include <random>
#include <type_traits>

using namespace std;

#define SHOW_VECTOR(v) {std::cerr << #v << "\t:";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOW_MAP(v){std::cerr << #v << endl; for(const auto& xxx: v){std::cerr << xxx.first << " " << xxx.second << "\n";}}

using LL = long long;

//------------------------------------------
//------------------------------------------

constexpr LL MAX = 1000000;

template<class T>
inline bool ISPRIME(const T x) {
    if (x <= 1)return false;
    for (T i = 2; i * i <= x; i++)if (x % i == 0)return false;
    return true;
}

template<class T>
vector<bool> ERATOSTHENES(const T n) {
    vector<bool> arr(n + 1, true);
    arr[0] = arr[1] = false;
    for (T i = 2; i * i <= n; i++) {
        if (arr[i]) {
            for (T j = i * 2LL; j <= n; j += i) {
                arr[j] = false;
            }
        }
    }
    return arr;
}

template<class T>
vector<T> ERATOSTHENES_VALUE(const T n) {
    vector<bool> primes = ERATOSTHENES(n);
    vector<T> results;
    for (int i = 0; i <= n; i++) if (primes[i]) results.emplace_back(i);
    return results;
}

// a <= x < b の素数を返す
template<typename T>
vector<bool> ERATOSTHENES(const T a, const T b) {
    vector<bool> small = ERATOSTHENES(b);
    vector<bool> prime(b - a, true);

    for (T i = 2; i * i <= b; i++) {
        if (small[i]) {
            for (T j = max(2LL, (a + i - 1) / i) * i; j < b; j += i) {
                prime[j - a] = false;
            }
        }
    }

    return prime;
}


int main() {

    int N;
    cin >> N;

    string S;
    cin >> S;

    string T = "";

    int ans = 0;
    for (auto c: S) {
        if (c == '3' or c == '5' or c == '7') {
            ans++;
        } else {
            T += c;
        }
    }

    for (int i = 0; i < T.size() - 1; i++) {
        if (T[i] == '1') {
            ans++;
            i++;
        }
    }

    cout << ans << endl;

//    auto primes = ERATOSTHENES_VALUE(MAX);
//    for (auto x: primes) {
//        string s = to_string(x);
//        bool good = true;
//        for (auto c: s) if ((c - '0') % 2 == 0)good = false;
//        if (good) {
//            cout << s << endl;
//        }
//    }

    return 0;
}