const input = require("fs").readFileSync("/dev/stdin", "utf8")

;(input => {
 
    const N = input - 0

    let ans = 0

    for (let i = 1; i <= N; i++) {
        n = Math.floor(N / i)
        ans += (n * n + n) / 2 * i
    }

    console.log(ans)
 
})(input)
