Given an input string containing only alphanumeric ASCII characters and starting with a letter, swap each letter run with the digit run which follows. A *run* is a sequence of consecutive letters or digits. Note that in the case where the input string ends with a run of letters, this run is left untouched. **Walk-through example** For instance, given the input string `uV5Pt3I0`: 1. Separate runs of letters and runs of digits: `uV 5 Pt 3 I 0` 2. Identify pairs of runs: `(uV 5) (Pt 3) (I 0)` 3. Swap pairs of runs: `(5 uV) (3 Pt) (0 I)` 4. Concatenate: `5uV3Pt0I` **Examples** uV5Pt3I0 -> 5uV3Pt0I J0i0m8 -> 0J0i8m abc256 -> 256abc Hennebont56Fr -> 56HennebontFr Em5sA55Ve777Rien -> 5Em55sA777VeRien nOoP -> nOoP This is [tag:code-golf] so the shortest answer in bytes wins. Explanations are encouraged.