The biggest number given in the swift test is Int.max, so if your solution happens to attempt to make a number higher than the input using normal Swift math operations, it will crash with an integer overflow error. It would be nice if the Swift test system printed the error that caused the crash, like it does in Xcode, but it doesn't.

Getting the following error when attempting this in Swift. Says all tests have passed but doesn't accept it as a solution

STDERR:
0 swift 0x00000000034bf568 llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 40
1 swift 0x00000000034c0146
2 libpthread.so.0 0x00007f6e2d68c330
3 libpthread.so.0 0x00007f6e2d9ff707
4 libpthread.so.0 0x00007f6e2da01031
5 libpthread.so.0 0x00007f6e2da021fa
6 libpthread.so.0 0x00007f6e2da0091b
7 libpthread.so.0 0x00007f6e2da022a5
8 libXCTest.so 0x00007f6e28a21641
9 libXCTest.so 0x00007f6e28a40460
10 libXCTest.so 0x00007f6e28a3d5c5
11 libXCTest.so 0x00007f6e28a3f806
12 libXCTest.so 0x00007f6e28a279e0
13 libXCTest.so 0x00007f6e28a215c5 TF6XCTest14XCTAssertEqualuRxs9EquatablerFTKzT_xKzT_xKT_SS4fileVs12StaticString4lineSu_T + 101
14 libXCTest.so 0x00007f6e2da00f79 TF6XCTest14XCTAssertEqualuRxs9EquatablerFTKzT_xKzT_xKT_SS4fileVs12StaticString4lineSu_T + 83753497
15 libXCTest.so 0x00007f6e2da02e90 TF6XCTest14XCTAssertEqualuRxs9EquatablerFTKzT_xKzT_xKT_SS4fileVs12StaticString4lineSu_T + 83761456
16 libXCTest.so 0x00007f6e2da0043e TF6XCTest14XCTAssertEqualuRxs9EquatablerFTKzT_xKzT_xKT_SS4fileVs12StaticString4lineSu_T + 83750622
17 libXCTest.so 0x00007f6e2da02fb5 TF6XCTest14XCTAssertEqualuRxs9EquatablerFTKzT_xKzT_xKT_SS4fileVs12StaticString4lineSu_T + 83761749
18 libXCTest.so 0x00007f6e28a546ab
19 libXCTest.so 0x00007f6e28a2b1a2
20 libXCTest.so 0x00007f6e28a54660
21 libXCTest.so 0x00007f6e28a543e0
22 libXCTest.so 0x00007f6e28a2a280 TFC6XCTest10XCTestCase10invokeTestfT_T + 112
23 libXCTest.so 0x00007f6e28a42219 TTSf4g_n___TFC6XCTest10XCTestCase7performfCS_9XCTestRunT + 313
24 libXCTest.so 0x00007f6e28a2a14e TFC6XCTest10XCTestCase7performfCS_9XCTestRunT + 14
25 libXCTest.so 0x00007f6e28a29f45 TFC6XCTest6XCTest3runfT_T + 629
26 libXCTest.so 0x00007f6e28a42ee5 TTSf4g_n___TFC6XCTest11XCTestSuite7performfCS_9XCTestRunT + 789
27 libXCTest.so 0x00007f6e28a433b3 TTSf4g_n___TFC6XCTest11XCTestSuite7performfCS_9XCTestRunT + 2019
28 libXCTest.so 0x00007f6e28a433b3 TTSf4g_n___TFC6XCTest11XCTestSuite7performfCS_9XCTestRunT + 2019
29 libXCTest.so 0x00007f6e28a2f6db _TF6XCTest7XCTMainFGSaT13testCaseClassMCS_10XCTestCase8allTestsGSaTSSFzS0_T_____Os5Never + 4283
30 libXCTest.so 0x00007f6e2d9ff0e9 _TF6XCTest7XCTMainFGSaT13testCaseClassMCS_10XCTestCase8allTestsGSaTSSFzS0_T_____Os5Never + 83692233
31 swift 0x0000000000c795f2 llvm::MCJIT::runFunction(llvm::Function*, llvm::ArrayRef) + 1042
32 swift 0x0000000000c7d0ff llvm::ExecutionEngine::runFunctionAsMain(llvm::Function*, std::vector > const&, char const* const*) + 1215
33 swift 0x000000000083ca6f swift::RunImmediately(swift::CompilerInstance&, std::vector > const&, swift::IRGenOptions&, swift::SILOptions const&) + 2303
34 swift 0x00000000008364f8
35 swift 0x0000000000831377 swift::performFrontend(llvm::ArrayRef, char const*, void*, swift::FrontendObserver*) + 2551
36 swift 0x00000000007f8788 main + 3016
37 libc.so.6 0x00007f6e2be35f45 __libc_start_main + 245
38 swift 0x00000000007f5e56
Stack dump:
0. Program arguments: /swift-vol/swift-gen/usr/bin/swift -frontend -interpret /tmp/swift117011-18-1bsoqew.jysvhrggb9/solution.swift -target x86_64-unknown-linux-gnu -disable-objc-interop -module-name solution