#include<fstream>
using namespace std;
int prim[2000003];
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int i, j, N, numar = 0;
		f>>N;
    for(i = 2 ; i <= N ; i++)
    prim[i] = 1;
    for(i = 2 ; i <= N ; i++)
        if(prim[i] == 1)
            {numar++;
                for(j= 2 * i ; j <= N ; j = j + i)
            prim[j] = 0;
            }
    g<<numar;
    return 0;
}