#include <bits/stdc++.h>
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int n;
bitset<2000001> a;

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

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