def f( m , r , n )
	a = m * pow( ( 1 + r ) , n )
	return a
end

def pow( x , y )
	a = 1;
	y.times { |i|
		a = a * x
	}
	return a
end

m = 10000
r = 0.05
p = 2
n = 1
while true do
	if f( m , r , n ) > ( m * p ) then
		break
	else	
		n += 1
	end
end
printf( "%d円を利率%3.2fで預けた時,元利合計は%d年後に%d円以上となります\n" , m , r , n , m*p )