"use strict";
function Main(input) {
    const series = [...Array(input).keys()].map(i => ++i);
    const amount = series.reduce((accum, current) => {
        return accum + current;
    }, 0);
    console.log(amount);
}
//テストの入力を受け取る
Main(require("fs").readFileSync("/dev/stdin", "utf8"));
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