Can anyone help me, which is more efficient while using in the for loop?

for(u = 2; u <= sqrt(n); u++)

or

for(u = 2; u*u <= n; u++)

Here are my both submission

Using first method — 119098252

Using second method — 119098208

While using the first method i got TLE but the same code using with the second method got Accepted..

I am assuming that method one is calculating sqrt(n) again and again and other one is calculating u*u again and again then why one is got accepted other one is not.

Please tell me the reason behind this?