#include<fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int main()
{
    int i,j,n,p=0;
    bool v[2000003];
    in>>n;
    for(i=2;i<=n;i++)
        v[i]=1;
    for(i=2;i<=n;i++)
        if(v[i])
        {
            p++;
            for(j=2;j<=n/i;j++)
                v[i*j]=0;
        }
        out<<p;
}