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

int main(){
  ll n, a = 0, b = 0;
  string s, t;
  cin >> s >> n;
  for (int i = 0; i < s.size(); i++){
    if (s[i] == '+') {
      if (a == 0) a = stoi(t);
      else if (b == 0) b = stoi(t); 
      t = "";
    } else {
      t += s[i];
    }
  }
  ll ans = (n * (2LL * a  + (n - 1) * (b - a))) / 2;
  cout << ans;
}