#include <bits/stdc++.h>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset<2000005>a;
int n;

int main()
{
    int i , j ;
    fin >> n;
    a[0] = a[1] = 1;
    for(i = 4; i <= n; i += 2)
        a[i] = 1;
    for(i = 3; i * i <= n; i += 2)
        if(a[i] == 0)
           for(j = i * i; j <= n; j += 2 * i)
              a[j] = 1;
    j = 0;
    for(i = 1; i <= n; i++)
        if(a[i] == 0) j++;

    fout << j << " ";

    return 0;

}