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#!/bin/bash

array=(4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 88 92 96 100)
target=$1

closest=${array[0]}
min_diff=$(( target > closest ? target - closest : closest - target ))

for value in "${array[@]}"; do
  diff=$(( target > value ? target - value : value - target ))
    if (( diff < min_diff )); then
        min_diff=$diff
            closest=$value
              fi
              done

              echo "$closest"