#include <bits/stdc++.h>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool v[2000001];

int main()
{
    int n,i,c=1,j;
    in>>n;
    for(i=3;i<=n;i+=2)
    {
        if(v[i]==0)
        {
            for(j=i*2;j<=n;j+=i)
            {
                 v[j]=1;
            }
            c++;
        }
    }
    out<<c;

    return 0;
}