let input = [

    // '3 4',
    // '1',
    // '5',
    // '9'


    '4 3',
    '1',
    '2',
    '3',
    '4',

];


let print = this.print || console.log;
let gets = this.gets || ((arr, index) => () => arr[index++])(input, 0);


let arr = gets().split(' ');


let numOfLines = Number(arr[0]);

let countOfConsNum = Number(arr[1]);


let min = 0;

let max = 0;

let avg = 0;

let arr2 = [];

let counter = 0;

let sum = 0;


for (let i = 0; i < numOfLines; i++) {


    let start = +gets();


    for (let j = start; j < countOfConsNum + start; j++) {

        arr2.push(j);

    }


    if (counter === 0) {

        min = Math.min(...arr2);

        sum += min;

    } else if (counter === 1) {

        max = Math.max(...arr2);

        sum += max;

    } else if (counter === 2) {

        avg = arr2.reduce((acc, el) => acc + el, 0);

        avg = avg / countOfConsNum;

        avg = Math.floor(avg);

        sum +=  avg;


    }

    arr2 = [];

    counter++;


    if (counter > 2) {

        counter = 0;

    }


}





print(sum);