#include <iostream>
#include <fstream>
using namespace std;
int a,b,n,nr=0,i,j;
char prim[2000005];
int main(void)
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;
    for (i = 2; i <= n; ++i)
        prim[i] = 1;
    for (i = 2; i <= n; ++i)
        if (prim[i])
        {
            ++nr;
            for (j = i+i; j <= n; j += i)
                prim[j] = 0;
        }
        cout <<nr;
    return 0;
}