Problems

# Superstitious Santa Claus

# Superstitious Santa Claus

How ‘s you know in different years interchange and different Santa Clauses transport the presents. But all of they are superstitious and transport presents all the year, except that days, when "Friday, 13" on the calendar of Santa Claus.

How many days Santa Claus wasn’t transport the presents during his duty?

**Input **

In the first line, the number **K** is the Santa Claus’s quantity shifts of duty.

Next in **K** lines through the gaps you can see years **A** and **B**, which hit on shifts.

**1920** ≤ **A** ≤ **B** ≤ **2050** (on the Gregorian calendar).

**Output**

One number is the quantity days, when Santa Claus will not transport the presents.

Input example #1

2 1999 2000 1991 1997

Output example #1

13