#include <iostream>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
bool v[2000001];

int main()
{
    int n,i,k,contor=0;
    cin>>n;
    for(i=2;i<=n;i++)
    {
        if(v[i]==0)
        {
            contor++;
            for(k=i+i;k<=n;k=k+i)
            {
                v[k]=1;
            }
        }
    }
    cout<<contor;
    return 0;
}