由于数据比较大n < 1e12，因此我们要用高精度

#include <bits/stdc++.h>
using namespace std;

vector<int> mul(vector<int> a, long long b) {
    vector<int> c;
    long long r = 0;
    for(int i = 0; i < a.size() || r; i ++ )
    {
        if(i < a.size()) r += (long long)a[i] * b;
        c.push_back(r % 10);
        r /= 10;
    }
    while(c.size() > 1 && c.back() == 0) c.pop_back();
    return c;
}

vector<int> div(vector<int> a, int b, int r) {
    vector<int> c;
    for(int i = a.size() - 1; i >= 0; i -- ) {
        r = r * 10 + a[i];
        c.push_back(r / b);
        r %= b;
    }
    reverse(c.begin(), c.end());
    while(c.size() > 1 && c.back() == 0) c.pop_back();
    return c;
}

int main() {
    string A;
    long long b = 0;
    cin >> A;
    vector<int> a;
    for(int i = A.size() - 1; i >= 0; i -- ) a.push_back(A[i] - '0');
    for(int i = 0; i < A.size(); i ++ ) b = b * 10 + (A[i] - '0');
    auto c = div(mul(a, (b + 1)), 2, 0);
    for(int i = c.size() - 1; i >= 0; i -- ) cout << c[i];
    return 0;
}