#include <bits/stdc++.h>
using namespace std;

int main(){
    ifstream input("ciur.in");
    ofstream print("ciur.out");
    bool prim[2000005];
    int n,ans=0;
    input>>n;
    memset(prim,true,sizeof(prim));
    for(int i=2;i<=n;++i)
       if(prim[i]){
           ++ans;
           for(int j=i+1;j<=n;j+=i)
               prim[j]=false;
       }
    print<<ans-1;
    input.close();
    print.close();
    return 0;
}