#include <bits/stdc++.h>
#define ll long long
#define x first
#define y second
#define pb push_back
using namespace std;
ifstream fin("ciur.txt");
ofstream fout("ciur.out");
ll n,i,j;
bool a[2000005];
int main(){
    fin>>n;
    ll ans=0;
    for(i=2;i<=n;i++)
        if(!a[i]){
                ans++;;
            for(j=i+i;j<=n;j+=i) a[j]=1;
        }

    fout<<ans;
}