#include<iostream>
#include<fstream>
#include<cstdio>
#include<algorithm>
#include<bitset>
using namespace std;
bitset<2000000> e;
int eratostene(int n)
{
    int cont=0;
    int i,j;
    for(i=2;i<=n;++i)
    {
        if(e[i]==0)
        {
            ++cont;
            for(j=2;i*j<=n;++j)
            {
                e[i*j]=1;
            }
        }
    }
    return cont;
}
int main()
{
    ifstream si;
    si.open("ciur.in");
    ofstream so;
    so.open("ciur.out");
    FILE* f=fopen("ciur.out","w");
    int n;
    si>>n;
    fprintf(f,"%i\n",eratostene(n));
}