A Japanese boy allegedly spent three weeks piecing back together a 10,000 yen bill like a jigsaw puzzle after it had been accidentally put through a paper shredder.

Japanese Twitter user ‘Tomo’ recently completed one of the hardest puzzles he’s ever done – putting back together a 10,000 yen ($65) bill that had been shredded into thousands of pieces. Apparently, his father accidentally shredded an old envelope at work after forgetting that he had put a 10,000 yen bill in it months ago. Realizing his mistake, the man decided to use his mistake as a challenging project for his son. He took home the entire shredder waste basket and told his son that if he could piece together the shredded bill and exchange it for a new one at the back, he could keep it. It was a daunting project for even the most avid jigsaw puzzle enthusiast, but one the boy gladly accepted.

Tomo began tackling his father’s challenge in mid-February, by sorting the bill pieces from the other bits of paper. It was harder than it sounds, as some parts of the bill had a lighter tone and could easily be mistaken for plain paper, and there was no way to tell if he found all the pieces.

Then, to give himself a better chance of completing the puzzle, he took another 10,000 yen bill and put it under a sheet of transparent plastic as a reference. Whenever he recognized a piece of the shredded bill, he set it on top of the whole bill to gauge his progress. Even so, working out where every piece fit was very difficult, and he ended up sinking over three weeks into the project.

On March 21st, Tomo shared a photo of the partially reconstructed bill, claiming that it was the best that he could do. It wasn’t perfect, there were bits missing from the lighter edges of the bill, and the rest of it wasn’t in much better shape. However, the Japanese youth was counting on the fact that the Bank of Japan has a very specific policy when it comes to exchanging damaged bills.

If more than 2/3 of a banknote remains, it can be exchanged for its full value. If the remaining area is between 2/5 and 2/3, it can be exchanged for half of its value, and if one comes with less than 2/5 of a banknote, it cannot be exchanged. Another important criterion is that the pieces must all belong to the same banknote and the unique number on it must be legible.

Tomo took the bill to the Bank of Japan at the end of last month, and even though the inspection of his shredded bill took a while he recently took to Twitter to inform his followers that he received a brand new 10,000 yen in exchange for his jigsaw puzzle, thanking the institution for being understanding.

Tomo’s project recently went viral on Japanese Twitter, with some users praising the youth for his patience and resolve, and others saying they wouldn’t have wasted three weeks of their time for 10 times the boy’s reward.