#include <fstream>

using namespace std;

ifstream fin ("ciur.in");
ofstream fout ("ciur.out");

    bool ciur[2000000];

int main()
{

    int n;


    fin >> n;

    ciur[1]=1;

    for(int i=4;i<=n;i+=2)ciur[i]=1;
    for(int i=3;i*i<=n;i+=2)
        if(ciur[i]==0)
        for(int j=i*i;j<=n;j+=2*i)ciur[j]=1;

    int s=1;


   for(int i=3;i<=n;i+=2)
    if(!ciur[i])s++;


    fout << s;


    return 0;
}