Runtime Error in python while calling function

While calling function defined in the program, the program is throwing Runtime Exception.

import math
import sys

def F(source,step,dist):
    if math.abs(source) > dist: return sys.maxsize
    elif source == dist: return step
    return min(steps(source+step+1,step+1,dist),steps(source-step-1,step+1,dist))

print F(0,0,5)