#include <bits/stdc++.h>

using namespace std;

#define rep(i, a, b) for (int i=a;i<(b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector <vi> vvi;


constexpr int LIM = 1e6;
constexpr int S = 1e3;
array<bool, LIM> isPrime{};
vi eratot() {
    constexpr int R = LIM / 2;
    vi pr = {2}, sieve (S+1);pr.reserve(int(LIM/log(LIM) * 1.1));
    vector<pii> cp;
    for(int i = 3; i <= S; i+=2) if(!sieve[i]) {
        cp.push_back({i, i * i / 2});
        for(int j = i*i; j <= S; j += 2 * i) sieve[j] = 1;
    }

    for(int L = 1 ; L <= R; L += S) {
        array<bool, S> block{};
        for(auto &[p, idx]: cp) {
            for(int i =idx; i < S+L; idx = (i+=p)) block[i-L] = 1;
        rep(i, 0, min(S, R - L))
            if(!block[i]) pr.push_back((L+i)*2 + 1);
        }
    }
    for(int i: pr) isPrime[i] = 1;

    return pr;
}

int get_next(int a) {
    vector<char> s;
    while(a > 0) {
        s.push_back('0' + (a % 10));
        a = a / 10;
    }

    s.pop_back();

    int number = 0;
    for(int idx = s.size() - 1; idx >= 0; idx--) {
        number = number * 10 + (s[idx] - '0');
    }
    return number;
}

vi primes;
bool is_prime(int n) {
    if(n < 2)
        return false;
    if(n < LIM)
        return isPrime[n];

    for(int p: primes) {
        if(n % p == 0)
            return false;
    }
    return true;
}

int main() {
    cin.tie(0)->sync_with_stdio(0);

    primes = eratot();
    int N;
    cin >> N;

    int curr = N;
    int m = 0;

    while(is_prime(curr)) {
        curr = get_next(curr);
        m++;
    }

    cout << m << endl;
}