#include <bits/stdc++.h>
#define ll long long
#define x first
#define y second
#define pb push_back
using namespace std;
ll n,i,j;
bool a[200005];
int main(){
    ifstream fin;
    fin.open("ciur.in");
    ofstream fout;
    fout.open("ciur.out");
    fin>>n;
    for(i=2;i<=n;i++){
        if(a[i]==0){
            for(j=i+i;j<=n;j+=i) a[j]=1;
        }
    }
    ll ans=0;
    for(i=2;i<=n;i++) if(a[i]==0) ans++;
    fout<<ans;
}