def f( x )
        a = 1
        (1..x).each { |i|
                a = a * i
        }
        return a
end

def comb( n , r )
	return f( n ) / ( f( r ) * f( n-r ) )
end

n = 10
r = 5
printf( "%dC%dは%dです\n" , n , r , comb( n , r ) )