Write a function that calculates and returns the nth Triangle Number, where n is the input parameter. You may assume that n is guarenteed to be positive. Note that nth Triangle Number is the sum of the first n positive integers. For example, the 5th Triangle Number is 15, since 1+2+3+4+5=15. (Note: no credit will be received if printf is used in this function). Please fill out the function definition below:

int triangle(int n){

}