A molecule is a chemical structure that is made up of more than one atom. H₂O is the molecule of water. It contains two hydrogen and one oxygen atoms. The weight of hydrogen is 1, and the weight of oxygen is 16. Thus the weight of water molecule is 2*1 + 16*1 = 18.

Question:
Write a program that calculates the mass of a molecule.

Input specification
The first line of the input contains an integer (n) that denotes the number of the atoms in the molecule where n i between 1 and 100. Each of the following n lines denotes an atom of the molecule with two integers. The first integer is the mass of the atom, and the second integer is the quantity of the atom.

Output specification
Show just one integer number: total weight of the molecule.