#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <string>
#include <queue>
#include <stack>
#include <math.h>
#include <set>
#define ALL(obj) (obj).begin(),(obj).end()
#define RALL(obj) (obj).rbegin(),(obj).rend()
#define P pair<int, int>

#define MOD 1000000007
#define INF 2147483647
#define NINF (-2147483647-1)
#define LLINF 9223372036854775807
using ll = long long;
using namespace std;

int main() {
    int N;
    cin >> N;
    vector<int> prime;
    vector<bool> p(N + 1, true);
    p[0] = p[1] = false;
    // エラトステネスのふるい
    for (int i = 2; i <= N; i++)
    {
        if (p[i]) {
            for (int j = i + i; j <= N; j += i)
            {
                p[j] = false;
            }
            prime.push_back(i);
        }
    }
    if (N < 2) {
        cout << -1;
        return 0;
    }
    //dp[i][j] := i番目までの素数を使ってjを作るときの足す回数の最大値
    vector<vector<int>> dp(prime.size(), vector<int>(N + 1, 0));
    dp[0][2] = 1;
    for (int i = 1; i < prime.size(); i++)
    {
        for (int j = 0; j <= N; j++)
        {
            dp[i][j] = dp[i - 1][j];
            if (j - prime[i] >= 0 && (dp[i - 1][j - prime[i]] != 0 || j == prime[i])) {
                dp[i][j] = max(dp[i][j], dp[i - 1][j - prime[i]] + 1);
            }
        }
    }
    int ans = dp[prime.size() - 1][N];
    if (ans == 0) {
        cout << -1 << endl;
    }
    else {
        cout << ans << endl;
    }
    getchar(); getchar();
    return 0;
}