Compare those strings

Chef has two strings $A$ and $B$ consisting of lowercase alphabets, each of length $N$. Help Chef in finding the number of indices $i$ $(1 \leq i \leq N)$ such that $A[i \dots N] \lt B[i \dots N]$. - $S[i \dots N]$ denotes the suffix of string $S$ starting at index $i$, i.e. $S_iS_{i+1}$ $\dots$ $S_{N}$. - String $S \lt$ String $T$ denotes that $S$ is lexicographically smaller than $T$. If two s