#include <iostream>
#include <fstream>

using namespace std;
char c[2000001];

int main()
{
    ifstream cin ("ciur.in");
    ofstream cout ("ciur.out");
    int i,j,n,cnt=0;

    cin>>n;
    for ( i = 2; i*i <= n; ++i)
    {
        if (c[i] == 0)
        {
            for (j = i*i; j <= n; j += i)
            {
                c[j] = 1;
            }
        }
    }
    for(i=2;i<n;i++)
    {
        if(c[i]==0)
        cnt++;
    }
    cout<<cnt;
    return 0;
}