#include <bits/stdc++.h>
using namespace std;
#define all(x) (x).begin(), (x).end()
using ll = long long;
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    string str;
    cin >> str;
    int n;
    cin >> n;
    int a = str[0] - '0', two = str[2] - '0';
    int d = two - a;
    int sum = ((2 * a + d * n - d) * n) / 2;
    cout << sum << endl;
    return 0;
}