#include<bits/stdc++.h>
using namespace std;
#define int             long long
#define pb              push_back
#define endl            '\n'
#define ff              first
#define ss              second
#define debug           cout<<"HERE"<<endl;
void edm()
{
    ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
    #ifndef ONLINE_JUDGE
    freopen("input.txt","r",stdin);
    freopen("outputtt.txt","w",stdout);
    #endif
}
void solve()
{
    string s;cin>>s;
    vector<int>v;
    int n;cin>>n;
    string cur = "";
    for(auto i:s)
    {
        if(i=='.')
        {
            if(cur.size())
            {
                int nn = stoll(cur);
                v.pb(nn);
            }
            cur = "";
            break;
        }
        else if(i!='+')
        {
            cur+=i;
        }
        else
        {
            if(cur.size())
            {
                int nn = stoll(cur);
                v.pb(nn);
            }
            cur = "";
        }
    }
    if(v.size()==1)
    {
        v.pb(v[0]+1);
    }
    int d = v[1] - v[0];
    int nth = v[0] + (n-1)*d;
    int sum = n * (v[0] + nth);
    sum = sum/2;
    // int sum = ((2*v[0] + (n-1)*d) * n)/2;
    cout<<sum<<endl;
}
int32_t main()
{
    //edm();
    int t = 1;
    // cin>>t;
    for(int i=1;i<=t;i++)
    {
        solve();
    }
}