The subroutine SUBSTRING extracts characters from a given string.

For example, SUBSTRING(2, 5, 'Algorithm') would return gori.

Figure 1 shows values assigned to four variables:

country ← 'United Kingdom'
capital ← 'London'
landmark ← 'Stonehenge'
river ← 'River Thames'

The variable $z$ is assigned a value using the statement:

$$z\leftarrow SUBSTRING(5,8,landmark)$$

Using Figure 1, what is the value of $z$?