#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{
    int n, i, j, k=0, c[2000001];
    in>>n;
    for (i=1; i<=n; i++)
    c[i]=0;
    for (i=2; i*i<=n; i++)
    {
        if (c[i]==0)
        {
            for (j=i*i; j<=n; j+=i)
            c[j]=1;
        }
    }
    for (i=2; i<=n; i++)
    if (c[i]==0)
    k++;
    out<<k;
    return 0;
}