<?php
function casalExponencial($i) {
    if ($i==1) {
        return 1;
    }
    if ($i==2) {
        return 1;
    }
    return casalExponencial($i - 1) + casalExponencial($i - 2);
}
$entrada = (int) trim(fgets(STDIN));
echo casalExponencial($entrada);
?>

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