#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int n,i,j;
    cin>>n;
    char prim[n+1];
    int nr=n-1;
    for(i=2;i<=n;i++)
        prim[i]=1;
    for(i=2;i*i<=n;i++)
        if(prim[i]==1)
            for(j=i*i;j<=n;j=j+i)
                {
                    prim[j]=0;
                    nr--;
                }
    cout<<nr;
    return 0;
}