#include <bits/stdc++.h>
using namespace std;
int ct, n, i, j;
bool w[2010000];
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f >> n;
    for(i = 2;i <= n;i++)
        if(w[i] == false)
        {
            ct++;
            for(j = i * i;j <= n;j = j + i)
                w[j] = true;
        }
    g << ct;
    return 0;
}