let i = require('fs').readFileSync('/dev/stdin', 'utf8').split('\n')
let r = i[1].split(' ').map((e) => parseInt(e))
let s = (r[1] - r[0]) / 2
let l = (r[1] + r[0]) / 2
console.log(i[0] * 2 * Math.PI * Math.PI * s * s * l)