#include <iostream>
#include <fstream>
#include <algorithm>
#include <bitset>
using namespace std;
bitset<2000003>a;
int main()
{
    int n, cnt , i, j;
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    fin>>n;
    a[1]=1;
    for(i=2;i*i<=n;i++)
      if(a[i]==0)//i-prim=>marchez cu multiplii lui i
        for (j=i*i;j<=n;j=j+i)
           a[j]=1;
    cnt=0;
    for(i=2;i<=n;i++)
        if (a[i]==0) cnt++;
    fout<<cnt;
    fout.close();
    return 0;
}