#include <iostream>
#include <fstream>


using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int prim[2000005];
int N,cnt;
int main()

{
    int i,j;
    f >> N;
    for (i = 2; i <= N; ++i)
        prim[i] = 1;
    for (i = 2; i <= N; ++i)
        if (prim[i])
        {
            ++cnt;
            for (j = i+i; j <= N; j += i)
                prim[j] = 0;
        }
       cout << cnt ;

    return 0;
}