60 before evaluating. Two practical methods follow.

Method 1 — Pisano reduction + iterative Fibonacci (recommended)

Intuition

Reduce the large indices n+2 and m+1 modulo 60 (Pisano period for modulus 10). Then compute the two Fibonacci values by iterating at most 60 steps.

Approach

Compute a = (n+2) % 60 and b = (m+1) % 60. If n or m are given as decimal strings, reduce them digit-by-digit: r = (r*10 + d) % 60.
Compute F(a) mod 10 and F(b) mod 10 by iterating up to 60 steps with x,y = y, (x+y) % 10.
Return (F(a) - F(b) + 10) % 10 to avoid negative digits.

Edge cases:

If m > n treat as invalid; if

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