Answer is 1046 tiles at 1 cm size
Step by step
We need to find surface area of 5 sides and add them together (no bottom was mentioned)
1 Top = 26 x 15 = 390
2 Short sides = 2(15 x 8) = 240
2 Long sides = 2(26 x 8) = 416
390 + 240 + 416 = 1046 sq cm
Divide your sq cm by size of tile
1046 / 1 = 1046 tiles
This is assuming no grout gap between tiles