- include <bits/stdc++.h>
using namespace std;
int jisuan(long long n) { for(long long i=2;i*i<=n;++i) if(n%i==0) return false;
return true;
}
int main()
{
long long n,sum=0;
cin>>n;
for(long long i=2;i<=n;++i)
if(jisuan(i)) ++sum;
cout<<sum; return 0; }