What is the most expensive letter?

"Spring Hope"

Author: Du Fu Era: Tang Genre: Five-Character Poetry

The country is broken by mountains and rivers, and the city is full of spring vegetation.

I shed tears when I am grateful for the flowers, and I hate the other birds.

The war rages on for three months, and a letter from home is worth ten thousand gold.

The white-headed scratches are shorter, and the lust is overwhelming.