Mike's phone blared out the musical motif that told him it was Ellie calling.

"What's up?", he said answering the call.

"You shouldn't just guess numbers until you get it right, you know!", shouted Ellie in his ear.

"The idea is to actually solve it ... using your brain!!", she added.

An image appeared on Mike's phone screen, accompanied by another annoying noise.

"You should find this one a little harder to guess", said Ellie with a touch of smugness in her voice.

Alan Turing Cryptography Competition 2023 is organised by the The Department of Mathematics at The University of Manchester.
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