#include <bits/stdc++.h>
#define N 2000005
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int ct, a[N], i, j, n;

void Ciur()
{
    a[2]=1;
    for(i=3; i<=n; i=i+2) a[i]=1; /// facem toate numere impare sa fie prime
    for(i=3; i*i<=n; i=i+2)
        if(a[i]==1)
            for(j=i*i; j<=n; j=j+2*i)
                a[j]=0;

}


int main()
{
    fin >> n;
    Ciur();
    for(i=1; i<=n; i++)
       if(a[i]==1)
          ct++;
    fout << ct;
    return 0;
}