#include <cmath>
#include <cstdio>
#include <map>
 
inline bool fermat_test(int n) {
    if (n < 2) {
        return false;
    } else if (n == 2) {
        return true;
    } else {
        return (static_cast<int>(std::pow(2, n - 1)) % n) == 1;
    }
}
 
inline bool prime_test(int n) {
    if (n < 2) {
        return false;
    } else if (n == 2) {
        return true;
    } else {
        for (int i = 3; i < static_cast<int>(std::sqrt(n)); i += 2) {
            if ((n %= i) == 0) {
                return false;
            }
        }
    }
    return true;
}
 
int main() {
    std::map<int, int> m;
    m[3] = 2;
    int n;
    while (~scanf("%d", &n)) {
        for (int i = 5; i <= n; i += 2) {
            if (m.count(i) > 0)
                continue;
 
            m[i] = m[i - 2] + (fermat_test(i) && prime_test(i));
        }
        printf("%d\n", m[n % 2 == 0 ? n - 1 : n]);
    }
}