Jones rule of 86

Have you ever tried maple syrup, a Canadian specialty? Even if you have never visited Canada, you may have poured some over pancakes.

Maple syrup, with its distinctive maple aroma and sweet taste, is made by boiling down the sap of sugar maple trees. The sap itself contains sugar and tastes sweet, so simply reducing it produces syrup.

Of course, it would be unrealistic to expect a tree to produce sap as sugary as thick syrup. Sugar maple sap has a sugar content of about $2$ Brix, while commercially sold maple syrup has a sugar content of at least $65$ Brix. A large amount of sap must be heated and reduced to make the maple syrup people love.

So how much sap must be boiled down to make $1$ gallon of syrup?

Nobody enjoys complicated concentration calculations. To estimate the amount of sap needed, Canadians came up with a simple formula called the Jones rule of 86:

Given the sugar content of sap in Brix, use the Jones rule of 86 to calculate how many gallons of sap are needed to make $1$ gallon of maple syrup.

The first line contains the sugar content of the sap in Brix, given with exactly one digit after the decimal point.

Print the amount of sap required according to the Jones rule of 86, rounded to one digit after the decimal point.

• $1.0 \le \text{sugar content of the sap} \le 10.0$