Write a program that outputs a histogram of grades for an assignment given to a class of students. The program should input each student’s grade as an integer and store the grade in a vector. Grades should be entered until the user enters −1 for a grade. Use a map from an int to an int to compute the histogram. The first integer in the map represents the grade, and the second integer represents the number of times that grade occurred. Output the histogram to the console. See Programming Project 5.7 for information on how to compute a histogram. There should be no restrictions on the minimum and maximum grade for this programming project.