How to deal with real large numbers which don't fit in 128 bits in Rust without loss?

When I try to do 10 power 100, I get

thread 'main' panicked at 'attempt to multiply with overflow', shorter.rs:33
note: Run with `RUST_BACKTRACE=1` for a backtrace.

which is normal because 10^100 is greater than 2^64 (and even 2^128).