#include <fstream>
#define N 2000001
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
bool a[N];
int prim[N];
int n;
int main()
{
    cin>>n;
    for (int i=4; i<=n; i+=2) a[i]=1; ///toate numerele pare cu exceptia lui 2

    for (int i=3; i*i<=n; i+=2)
        if (a[i]==0)
            for (int j=i*i; j<=n; j=j+2*i)
                a[j]=1;
    int k=0;
    prim[++k]=2;
    for (int i=3; i<=n; i+=2)
        if (a[i]==0) prim[++k]=i;
    int nr=0;
    for (int i=1; i<=k; ++i)
        nr++;
    //cout<<prim[i]<<" ";
    cout<<nr;
    cin.close();
    cout.close();
    return 0;

}