#include <fstream>

using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

bool v[2000005];

int main()
{
    int n,i,j,s = 0;
    cin >> n;
    v[1] = 1;
    v[0] = 1;
    //for(i = 4; i <= n; i = i + 2)
    //    v[i] = 1;
    for(i = 2; i <= n; i++)
        if(!v[i])
        {
            for(int j = i*i; j <= n; j = j + i)
                v[j] = 1;
            s++;
        }
    cout << s;
    return 0;
}