#include <bits/stdc++.h>

using namespace std;


bool a[2000005];
int n;

void ciur(int c)
{
    int i, j;
    for(i = 3; i * i <= c; i += 2)
    {
        if(a[i] == false)
        {
            for(j = i * i; j <= c; j += 2 * i)
                a[j] = true;
        }
    }
    int k = 1;
    for(i = 3; i <= c; i += 2)
    {
        if(a[i] == false)
        {
            k++;
        }
    }
    fout << k;
}

int main()
{
    fin >> n;
    ciur(n);
    return 0;
}