```ts
/**
 * The nth Fibonacci number, modulo 1000000007.
 */
export function fibMod(n: number): number {
  if (n < 2) {
    return n;
  }

  let a = 0, b = 1;
  for (let i = 2; i <= n; i++) {
    let next = (a + b) % MODULUS;
    a = b;
    b = next;
  }

  return b;
}
```