#include <bits/stdc++.h>
#define fast ios::sync_with_stdio(false)
#define ct cin.tie(nullptr)
#define ll long long
#define nl '\n'
#define newline cout<<'\n'
#define yes cout<<"YES"<<'\n'
#define no cout<<"NO"<<'\n'
using namespace std;
void solve()
{


}
int main()
{
    fast;
    ct;
   //int t;
    //cin>>t;
    //while(t--)

        string s;
        getline(cin,s);
        int n;
        cin>>n;
        int num_cnt=0;
        int dot_cnt=n-2;
        vector<int>arr;
        for(int i=0; i<s.size();i++)
        {
            if(s[i]>='0' && s[i]<='9')
            {
                num_cnt++;
                int num=s[i]-'0';
                arr.push_back(num);
            }
            if(num_cnt==2)
                break;
        }
        ll dif = arr[1]-arr[0];
        ll sum=arr[0]+arr[1];
        int last=arr[1];
        for(int i =0; i<dot_cnt;i++)
        {
            last=last+dif;
            sum+=last;

        }
        cout<<sum<<nl;
}