#include<cstdio>
#include <vector>
#include <cstring>
/* #include "Euclid.cpp"
#include "EuclidExtended.cpp"
#include "LCS.cpp"
#include "RabinKarp.cpp"
#include "KMP.cpp"
#include "Arbint.cpp" */
using namespace std;

class Eratosthenes {

#define NMAX 2000000+1

private:
    int N;
    bool s[NMAX];

public:

    void eratosthenes_main() {
        freopen("ciur.in", "r", stdin);
        freopen("ciur.out", "w", stdout);

        scanf("%d", &N);

        int sol = 0;

        for (int i = 2; i <= N; i++)
            if (!s[i]) {
                sol++;
                for (int j = i; j <= N; j += i)
                    s[j] = true;
            }


        printf("%d", sol);

    }

} eratosthenes;

int main()
{
    eratosthenes.eratosthenes_main();
    return 0;
}