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

#define ll long long
#define endl '\n'

void Try() {
    string S; cin >> S;
    int n; cin >> n;
    string a ="", b = "";
    int cnt = 0;
    for (int i = 0; i < S.size(); i++) {
        char c = S[i];
        if (c == '.') break;
        if (c == '+') cnt++;
        if (cnt >= 2) break;
        if (cnt < 1) {
            a += c;
        }
        else b += c;
    }
    
    int x = stoi(a); int y = stoi(b);
    ll dif = y - x;
    ll z = x + 1LL * (n - 1) * dif;
    
    cout << 1LL * (n * (x + z)) / 2 << endl;
    
}

int32_t main() {
    ios_base::sync_with_stdio(0); cin.tie(0);

    int t = 1;
    //cin >> t;
    for (int i = 1; i <= t; i++) {
        Try();
    }

}