For the following code I'm getting the following error: line 15

"Ambiguity between 'std::sqrt(double)' and 'sqrt(double)' in function main()"

I compared the code with my friend's and they were practically identically. Yet, his got no errors. I copied and pasted his code, compiled it, and ran it. It got the same ambiguity error! The assignment itself is just a square root function and that's not the problem. The code is below:

Code:#include<iostream> using namespace std; double sqrt(double x){ double counter = 1; double guess = 1; while (counter < 20){ guess = (guess + (x/guess))/2; counter = counter + 1; } return guess; } int main(void){ double a; cin >> a; cout << sqrt(a); return 0; }