The work done by a person when he climbs to a higher level is equivalent to the increase in the potential energy of the person. Assume that the person can walk at 100% efficiency and all the work done is converted to gravitational potential energy.
When the person with mass 125 kg climbs a height of 65 m, the increase in the gravitational potential is 125*65*9.8 = 79625 J.
One Joule = 0.239005736 calories, 79625 J = 18.544 KCal.
The number of calories burnt by the person in climbing to his flat as 18.544 kcal.