Find the time complexity of sum of two numbers using function

What is the time complexity of the program for the sum of two numbers using function ?

Step count method

int sum() 
{
int a,b,c; // —-0
a=10; //—-1
b=20; //—-1
c=a+b; //—-1
return c; //—-1
}
f(n) = 0+1+1+1+1 = 4
f(n) = O(1)