#include<bits/stdc++.h>
using namespace std;
#define rc(x) return cout<<x<<endl,0
#define pb push_back
#define dbg(x) cout << #x << '=' << x << '\n';
#define ll long long
#define sz size()
#define x first
#define y second
#define pi pair <int, int>
#define pii pair <int, pi>
#define vi vector <int>
const ll mod = 1e9 + 7;
int n, cnt;
bool pr[2000002];

int32_t main(){
    ios_base :: sync_with_stdio(0); cin.tie(); cout.tie();
    ifstream cin("ciur.in");
    ofstream cout("ciur.out");
    cin>>n;
    cnt++;
    for(int i=3; i<=n; i+=2){
            //if(i==5001) cout<<"xd"<<endl;
        if(pr[i]==0){
            cnt++;
            if(1LL*i*i<=1LL*n) for(int j=i*i; j<=n; j+=i) pr[j]=1;
        }
    }
    cout<<cnt;
}