Building roads in the mountains is extremely difficult, costly and even in some places impossible.
Барои Худо ҳеҷ чизи ғайриимкон нест.
For God nothing is impossible
имкон: possibility (noun)
The prefix ғаири means “without”, “outside” or “except for” so you can think of ғайриимкон as “without possibility”.
Other words with suffix ғаири –
ғайримактабӣ: extra-curricular, outside of school
ғайрикорӣ: outside of work (or working hours)
ғайрикофӣ: not enough, insufficient
ғайримаҷбурӣ: without force, non-compulsory