Two numbers can be fused by putting one in front of the other to make the largest number possible. For example, 29 and 71 can be fused to form 7129.

A list of numbers can be fused by repeatedly fusing pairs of numbers of the same length to form the biggest number possible.

For example, given the sequence 1 3 4 2, the 1 and 3 are fused to give 31 and the 4 and 2 are fused to give 42. Then the 31 and 42 are fused to give 4231.

**Question**:

If the original sequence is 4 5 3 6 7 2 9 4 5 6 4 7 8 2 1 5, what is the last digit of the final fused number?