#include <iostream>
#include <fstream>

using namespace std;

bool v[2000010];
int ciur[1000000],nciur;

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int N;
    f>>N;
    f.close();
    ciur[++nciur]=2;
    for(int i=3;i<=N;i+=2)
    {
        if(v[i]==false)
        {
            ciur[++nciur]=i;
            if(1LL*i*i<=N*1LL)
                for(int k=i;k*i<=N;k+=2)
                    v[k*i]=true;
        }
    }
    g<<nciur<<"\n";
    g.close();
    return 0;
}