#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++;
            else
                for(int j=i;j<=N;j+=i)
                    s[i]=true;

        printf("%d",sol);

    }

} eratosthenes;

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