#include <fstream>

using namespace std;

ofstream fout("ciur.out");
int n, ciur[2000003];

int main()
{
    ifstream fin("ciur.in");
    fin >> n;
    fin.close();
    for(int i = 4; i <= n; i += 2)
        ciur[i] = 1;
    for(int i = 3; i * i < n; i += 2)
        if(ciur[i] == 0)
        for(int j = i  * i; j <= n; j += 2 * i)
            ciur[j] = 1;
    int cnt = 0;
    for(int i = 2; i <= n; i++)
        if(!ciur[i])
            cnt++;
    fout << cnt << "\n";
    fout.close();
    return 0;
}