// for AtCoder
"use strict";(function(){let t,n,i;this.input?t=this.input:require&&(t=require("fs").readFileSync("/dev/stdin","utf8"));let e=0;this.debug=function n(i){"object"==typeof i?n(i[0]):t=i.trim()},this.next=s,this.nextNumber=function(){return+s()},this.write=function(t){void 0===t&&(t="");var n=(r+=t).match(/([\s\S]*)\n([^\n]*)/);n&&(log(n[1]),r=n[2])},this.flush=function(t){void 0===t&&(t="");""!=(r+=t)&&(log(r),r="")},this.getLine=function(){n||(n=t.split(/[\n\r]+/));return i=null,n[o++]},this.log=console.log.bind(console),this.err=console.error.bind(console);let o=0,r="";function s(){return n||(n=t.split(/[\n\r]+/)),(!i||i.length-1<=e)&&(e=0,i=n[o++].split(/\s+/)),i[e++]}function u(t,n,i){for(var e=t;e<n&&i(e)!==BREAK;e++);}function l(t,n,i){for(var e=n-1;e>=0&&i(e)!==BREAK;e--);}this.FOR=u,this.RFOR=l,this.REP=function(t,n){u(0,t,n)},this.RREP=function(t,n){l(0,t,n)},this.CONTINUE=0,this.BREAK=1,this.range=function t(n,i){if(void 0===i)return t(0,n);return Array.apply(null,{length:i-n}).map((t,n)=>n)},"function"==typeof main&&main()}).call(global);
//
let n=next()
log(n*(n+1)/2)