const lines = require('fs')
  .readFileSync('/dev/stdin', 'utf-8')
  .trim().split('\n').values();

const C = Number(lines.next().value);
const [Rin, Rout] = lines.next().value.split(' ').map(x => Number(x));

const c = Math.PI * (Rout + Rin);
const a = Math.PI * (((Rout - Rin) / 2) ** 2);

console.log(c * a * C);