#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool prim[2000000];
int main()
{int i,n,j,cnt=0;
    in>>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;
        }
    out<<cnt;
    
   return 0;
}