unittest
{
	assert( [ "432" ].parse.expand.solve == "400" );
	assert( [ "1079" ].parse.expand.solve == ":(" );
	assert( [ "1001" ].parse.expand.solve == "927" );
}



import std.conv;
import std.range;
import std.stdio;
import std.typecons;

void main()
{
	stdin.byLineCopy.parse.expand.solve.writeln;
}

auto parse( Range )( Range input )
if( isInputRange!Range && is( ElementType!Range == string ) )
{
	auto n = input.front.to!( long );
	return tuple( n );
}

auto solve( long n )
{
	for( auto i = 0L; i <= n; i++ )
	{
		if( cast( long )( i * 1.08 ) == n ) return i.to!( string );
	}
	return ":(";
}
