unittest
{
	assert( [ "2", "10 30" ].parse.expand.solve == "7.50000" );
	assert( [ "3", "200 200 200" ].parse.expand.solve == "66.66667" );
	assert( [ "1", "1000" ].parse.expand.solve == "1000.00000" );
}



import std.conv;
import std.format;
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 ) )
{
	input.popFront;
	auto as = input.front.split.to!( long[] );
	return tuple( as );
}

auto solve( long[] as )
{
	auto t = 0.0;
	foreach( a; as )
	{
		t += 1.0 / a;
	}
	return format( "%0.5f", 1.0 / t );
}
