#include <fstream>
#include <vector>

using namespace std;

ifstream fin("era.in");
ofstream fout("era.out");
int n;
int main(void)
{
    int i, j;
    long cnt = 0;
    fin>>n;
    bool *prim = new bool [n]();
    for (i = 2; i <= n; ++i)
        if(!prim[i])
        {
            ++cnt;
            for (j = i+i; j <= n; j += i)
                prim[j] = true;
        }
    fout<<cnt;
    return 0;
}