#include <bits/stdc++.h>
#define M 2000000

using namespace std;

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

long long int n, i, j, nr;
int v[M + 5], cnt;

void read()
{
    f >> n;
    f.close();
}

void solve()
{
   for (int i=2; i<=n; i++)
    if (v[i] == 0)
   {
       ++cnt;
       for(j=2*i; j<=n; j+=i)
        v[j] = 1;
   }
   g<<cnt;
   g.close();
}

int main()
{
    read();
    solve();
    return 0;
}