Note that there is a single quaver before the first bar line. This is called an anacrusis or upbeat and is a weak beat, allowing the emphasis to be placed on the first syllable of ‘Mississippi’, on the first beat of the bar. When numbering bars, the first full bar is counted as bar 1. Throughout the song, many of the phrases start on an anacrusis, whether it be a quaver, crotchet, minim, etc.