#include<fstream>

using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
int n,i,j,v[2000000]={0},nr;
int main ()
{
    fin>>n;
    if(n<=1)
        nr=0;
    else
        nr=1;
    for(i=3;i*i<=n;i+=2)
    {
        if(v[i]==0)
        for(j=2;j<=n/i;j++)
        v[i*j]=1;
    }
    for(i=3;i<=n;i+=2)
        if(v[i]==0)
        nr++;
    fout<<nr;
    return 0;

}