unittest
{
	assert( [ "uncopyrightable" ].parse.expand.solve == "yes" );
	assert( [ "different" ].parse.expand.solve == "no" );
	assert( [ "no" ].parse.expand.solve == "yes" );
}



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

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

auto parse( Range )( Range input )
if( isInputRange!Range && is( ElementType!Range == string ) )
{
	auto s = input.front.strip.to!( dchar[] );
	return tuple( s );
}

auto solve( dchar[] s )
{
	return ( s.sort().group.count!( ( a ) => 2 <= a[ 1 ] ) == 0 ) ? "yes" : "no";
}
