#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset<2000001>a;
int cnt;

void Ciur(int n)
{
    int i,j;
    a[1] = a[0] = 1;
    for(i = 4; i <= n; i += 2)
        a[i] = 1;
    for(i = 3; i * i <= n; i += 2)
        if(a[i] == 0)
            for(j = i * i; j <= n; j += 2 * i)
                a[j] = 1;
    for(i = 1; i <= n; i++)
        if(a[i] == 0) cnt++;
}

int main()
{
    int n;
    fin >> n;
    Ciur(n);
    fout << cnt;
    return 0;
}