Weighted Average Calculator

You are tasked with calculating the weighted average of a list of grades for students. Each student has a grade and a weight associated with that grade. Input consists of an integer N followed by N pairs of integers where the first integer is the grade and the second integer is the weight. The output should be a single float representing the weighted average rounded to two decimal places. Example: Input: 3 80 2 90 3 70 5 Output: 79.38