#include <fstream>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

char prim[2000000];
int N,i,j,cnt;
int main()
{
    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;
        }
    g<<cnt;
}