A man is passing barrels of water to another person from a height of 7 meters. The barrel is attached to a roof that is 10 meters above the ground. The rope holding the barrel is 8 meters long and will break if the tension exceeds 638 N. How many liters of water can the man put in the barrel without the rope breaking (assuming that the barrel is massless)? (The density of water = 1000 kg/m3 and 1 m3 = 1000 L. Density = mass/volume.)