/// ciurul
#include <iostream>
#include <fstream>
#include <utility>
#include <algorithm>
#define NMax 2000001
///#define f cin
///#define g cout
using namespace std;

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

int ans;
int n;
bool prim[NMax];

int main()
{
    f >> n;
    for(int i = 2; i <= n; ++i)
        prim[i] = 1;
    for(int i = 2; i <= n; ++i)
        if(prim[i])
        {
            ++ans;
            for(int j = i + i; j <= n; j += i)
                prim[j] = false;
        }
    g << ans << '\n';
    return 0;
}