#include <fstream>

using namespace std;

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

#define nmax 2000005

int n,nr;
char prim[nmax];

int main()
{
    fin>>n;
    for(int i=2;i<=n;++i)
        prim[i]=1;
    for(int i=2;i<=n;++i)
        if(prim[i])
            {nr++;
            for(int j=i+i;j<=n;j+=i)
                prim[j]=0;}
    fout<<nr;
    return 0;
}