#include <iostream>
#include <bits/stdc++.h>
#include <vector>
using namespace std;


const int MAXSIZE = 1000000 / 2 + 1;
std::vector<wchar_t> p(MAXSIZE);

int getTheNumber(int n);
int ciur (int n){
    int i,j,nr=1;
    for(i=1;(i<<1)+1<=n;i+=1){
        if(p[i]==0){
            nr++;
            for(j=i+i+i+1;(j<<1)+1<=n;j+=(i<<1)+1)
            p[j]=1;
        }
    }
    return nr;
}


int main()
{
    int N;
    ifstream f ("ciur.in");
    ofstream g ("ciur.out");
    f>>N;
    g<<ciur(N);
    return 0;
}