[UVa] 10830 - A New Function

#include <set>
#include <map>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <cctype>
#include <cstdio>
#include <string>
#include <vector>
#include <cassert>
#include <cstdlib>
#include <cstring>
#include <sstream>
#include <iostream>
#include <algorithm>

typedef unsigned long long ull;
typedef long long xll;
typedef long double ld;

using namespace std;
ull sumfind(ull a, ull n)
{
    return ((n*(n+1)/2) - (a*(a-1)/2));
}
ull csod(ull n)
{
    ull root = (ull)sqrt((double)n), i, j;
    ull lim, sum=0;

    for (i=2 ; i<=root ; i++)
    {
        lim = n/i;
        sum += (sumfind(i+1,lim) + (i*(lim-i+1)));
    }

    return sum;
}

int main()
{
    ull n, sum=0, kase=1;

    while (cin >> n && n)
    {
        cout << "Case " << kase++ << ": " << csod(n) << endl;
    }
    return 0;

}