process.stdin.resume();
process.stdin.setEncoding('utf8');

var lines = [];
var reader = require('readline').createInterface({
    input: process.stdin,
    output: process.stdout
});
reader.on('line', (line) => {
    lines.push(line);
});
reader.on('close', () => {
    
    const n = Number(lines[0]);
    let ans = 0;
    
    for (let i = 1; i <= n; i++) {
        ans += i;
    }
    console.log(ans);
    
});