#include <iostream>
#include <deque>
#include <vector>
#include <cstring>
#include <algorithm>
using namespace std;

int N, compus[2000010], i, j, sol;

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d", &N);
    sol = 1;
    for(i = 3; i <= N; i+=2)
    {
        if(compus[i] == 0)
        {
            sol = sol  + 1;
            if(i > 2000)continue;
            for(j = i * i ; j <= N; j+=i)
                compus[j] = 1;
        }
    }
    cout<<sol<<"\n";
    return 0;
}