题解 | #等差数列#

const rl = require("readline").createInterface({ input: process.stdin });
var iter = rl[Symbol.asyncIterator]();
const readline = async () => (await iter.next()).value;

void async function () {
    // Write your code here
    while(line = await readline()){
        let n = Number(line);
        let a1 = 2,d=3;
        let result = n*(n-1)*d/2 + n*a1;//等差数列前n项的和
        console.log(result);
    }
}()