What is the run time of the following statement in big oh notation?

public int foo ( int x , int k ) {
     if ( x <= k )
         return 1;
     else
         return foo ( x / k , k ) + 1;
}

From my understanding, the runtime of this should equal the runtime of the conditional + the runtime of the larger if/else statement.

However, I'm having trouble determining the correct runtime of the statement "return foo(x/k, k) + 1". Would this be constant? The increase of x and k doesn't seem to have an effect on the runtime, as it is the ratio between them that is important for the outcome.

Any clarity would be much appreciated. Thanks!