var BigInt = require('big-integer');

function sqrt(c) {
  if (c.isZero()) {
    return c;
  }
  if (c.lesser(4)) {
    return BigInt(1);
  }

  var n, p;
  var high = c.shiftRight(1);
  var low = BigInt.zero;

  while (high.greater(low.add(1))) {
    n = high.add(low).shiftRight(1);
    p = n.square();
    if (c.lesser(p)) {
      high = n;
    } else if (c.greater(p)) {
      low = n.equals(1) ? n.add(1) : n;
    } else {
        break;
    }
  }
  if (c.equals(p)) {
    return n;
  } else if (c.equals(high.square())) {
    return high;
  }
  return low;
}