#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <vector>
#include <set>
#include <cmath>


//#define MAX_N  1000000001

bool is_prime(int n){
    for(int i = 2; i < n; i++){
        if((n % i) == 0){
            return false;
        }
    }
    return true;
}

void search(std::string curr_str, int depth, int *max_depth){
    if(curr_str.empty()  || !(is_prime(std::stoi(curr_str))))
    {
        *max_depth = std::max(depth, *max_depth);
        return;
    }

    for(int i = 0; i < curr_str.size(); i++){
        std::string new_str("");
        for(int j = 0; j < curr_str.size(); j++){
            if(j != i){
                new_str += curr_str[j];
            }
        }

        if(!(new_str.empty())) {
            new_str = std::to_string(std::stoi(new_str));
        }
        search(new_str, depth + 1, max_depth);
    }
}


int main() {

    char *in_str = NULL;
    scanf("%ms", &in_str);
    std::string s(in_str);

    int MAX_N = std::stoi(in_str) + 1;

    /*
    bool *is_prime = (bool *)malloc(sizeof(bool) * MAX_N);
    memset(is_prime, true, sizeof(bool) * MAX_N);

    is_prime[0] = false;
    is_prime[1] = false;

    for(int i = 2; i < sqrt(MAX_N); i++){
        if(is_prime[i]){
            for(int j = i + i; j < MAX_N; j += i){
                is_prime[j] = false;
            }
        }
    }
     */

    //std::vector<char> in_vec;
    //char tmp;

    /*
    char *in_str = NULL;
    scanf("%ms", &in_str);
    std::string s(in_str);
    */
   // std::set<int> primes_found;
    int max_depth = 0;
    search(in_str, 0, &max_depth);

    printf("%d\n", max_depth);

    free(in_str);
    in_str = NULL;

    //free(is_prime);
    //is_prime = NULL;

    return 0;
}