/*
    Keep It Simple!
*/

#include<fstream>
using namespace std;

int N;
bool prim[2000005];

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");

    f >> N;
    int cnt = 1;
    for(int i=3;i<=N;i+=2)
    {
        if(!prim[i])
        {
            cnt++;
            for(int j=i;j<=N;j+=i)
                prim[j] = 1;
        }
    }

    g << cnt;
}