#include <bits/stdc++.h>

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

int n, nr = 1, a[2000005];

int main()
{
    fin >> n;
    for(int  i = 4; i <= n; i += 2) a[i] = 1;
    for(int  i = 3; i * i <= n; i += 2)
        if(a[i] == 0)
        for(int j = i * i; j <= n; j = j + 2 * i)
        a[j] = 1;
    for(int i = 3; i <= n; i+=2) if(a[i] == 0) nr++;

    fout << nr;
    return 0;
}