#include <iostream>
#include <cmath>
#include <set>
#include <sstream>
#include <queue>

int strToNum(std::string str) {
    int ret = 0;
    std::istringstream stream(str);
    stream >> ret;
    return ret;
}

bool isprime(int num) {
    if (num == 1 || num == 0)
        return false;
    if (num == 2)
        return true;
    for (int i = 2; i <= int(sqrt(num) + 1); ++i) {
        if (num % i == 0)
            return false;
    }
    return true;
}

int main() {
    std::string numStr;
    std::cin >> numStr;
    int startNum = strToNum(numStr);

    int maxCount = 0;
    std::set<std::pair<std::string, int>> visited;
    std::queue<std::pair<std::string, int>> queue;
    queue.push({numStr, 0});
    visited.insert({numStr, 0});
    while (!queue.empty()) {
        std::string currentStr = queue.front().first;
        int currentCount = queue.front().second;
        queue.pop();
        int currentNum = strToNum(currentStr);

        if (isprime(currentNum)) {
            // std::cout << currentNum << std::endl;
            ++currentCount;
        } else {
            if (currentCount > maxCount)
                maxCount = currentCount;
            continue;
        }

        for(int i = 0; i < currentStr.length(); i++)
        {
            std::string novy(currentStr);
            novy.erase(i, 1);
            int xxxx = strToNum(novy);
            novy = std::to_string(xxxx);
            if(visited.insert({novy, currentCount}).second)
                queue.push({novy, currentCount});
        }

    }

    std::cout << maxCount << std::endl;

    return 0;
}