def truckTour(petrolpumps):

petrolRest = [pump[0]-pump[1] for pump in petrolpumps] * 2

for i in range(len(petrolpumps)):

    tank = 0

    for j in range(i, i + len(petrolpumps)):

        tank += petrolRest[j]

        if tank < 0: break     

    if tank < 0: continue

    else: return i

return -1