#include <bits/stdc++.h>
#define ll long long
#define x first
#define y second
#define pb push_back
using namespace std;
int main(){
    ifstream fin;
    fin.open("ciur.in");
    ofstream fout;
    fout.open("ciur.out");
    ll n,i,j;
    vector< ll> v ;
    fin>>n;
    v.pb(2);
    for(i=3;i<=n;i++){
            ll p=0;
        for(j=0;j<v.size();j++){
            if(i%v[j]==0) p=1;
        }
    if(p==0) v.pb(i);
    }
    fout<<v.size();
}