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

#define ll long long
#define endl '\n'
#define print(v) for(auto e:v) cout<<e<<" "; cout<<endl;

void solve() {
    string s ; cin >>s;
    int n; cin >> n ;
    ll cnt = 0;
    ll nts = s.size();
    string aa = "";
    string bb = "";
    for(int i = 0; i < nts ; i++ ) {

        if(cnt >0){
            if(s[i] == '+'){
                break;
            }
            if(s[i]!='+'){
                bb += s[i];
            }

        }
        else if(s[i] != '+') {
            aa +=s[i];
        }
        else{
            cnt++;
        }
    }
    ll a = stoll(aa);
    ll b = stoll(bb);
    ll dif =  b - a;
    ll ki = (n - 1) * dif;
    ki +=  (2 * a);
    ki *= n;
    ki /= 2;
    cout << ki << endl;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int t = 1;// cin >> t;
    while(t--){
        solve();
    }
    return 0;
}