#include <bits/stdc++.h>

using namespace std;

int n;

const int N = 2000001;

bool sv[N + 1];

int main()
{
    ifstream cin("ciur.in");
    ofstream cout("ciur.out");
    cin >> n;
    sv[0] = sv[1] = 1;
    for(int i = 2; i * i <= n; i++)
    {
        if(sv[i] == 0)
        {
            for(int j = i * i; j <= n; j += i)
                sv[j] = 1;
        }
    }
    int p = 0;
    for(int i = 2; i <= n; i++)
    {
        if(!sv[i])
            p++;
    }
    cout << p;
    return 0;
}