#include <iostream>
#include <fstream>

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

int sir[1000001];

int main()
{
    long long x, n, i, c=0;
    fin>>n;
    for(i=2;i<=n;i++)
        {
            if(sir[i]==0)
                c++;
            if((i*i)<=n)
            {
                for(int j=i+i;j<=n;j+=i)
                sir[j]=1;
            }
        }
    fout<<c;
    return 0;
}