#include<bits/stdc++.h>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,v[200000],nr;

int main()
{   cin >> n;
    for (int i = 2;i <=n; i++){
        if(v[i]==0){
            for( int j = i+i;j<=n;j+=i)
                v[j]=1;
           nr++;
        }

    }
    cout<<nr;
    return 0;
}