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

long N,i,j,prim=0;
bool c[2000001];

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

    in>>N;
    for(i=2;i*i<=N;i++)
        if(!c[i])
            for(j=i*i;j<=N;j+=i)
                c[j]=true;
    for(i=2;i<=N;i++)
        if(!c[i])
            prim++;
    out<<prim;
    return 0;
}