#include <fstream>
#include <bitset>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int n,i,j,nr;
bitset<2000001>v;
int main()
{
    in>>n;
    v[1]=1;
    nr=1;
    for(i=4; i<=n; i+=2) v[i]=1;
    for(i=3; i<=n; i+=2)
        if(v[i]==0)
        {
            nr++;
            for(j=i; j<=n/i; j+=i)
                v[i*j]=1;
        }
    out<<nr;
}