#include <iostream>

using namespace std;
int cnt=-1,c[100000];
int main()
{
    unsigned long long i, j;
    int n;
    cin>>n;
    for ( i = 2; i*i <= n; ++i)
    {
        if (c[i] == 0)
        {
            for (j = i*i; j <= n; j += i)
            {
                c[j] = 1;
                cnt++;
            }
        }
    }
    cout<<cnt;
    return 0;
}