#include <bits/stdc++.h>
using namespace std;
#define fast ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define ll long long
int main()
{
    fast
    /*ll t;
    cin>>t;
    while(t--) solve*/

    string s;
    vector<int>a;
    ll n, sum=0;
    cin>>s>>n;

    for (int i=0; i<s.size(); i ++){
        if (isalnum(s[i])) {
            int num=s[i]-'0';
            a.push_back(num);
        }
    }

    int d = a[1]-a[0];
    int f=a[0];
    for(int i=0; i<n; i++){
        sum+=f;
        f+=d;
    }

    cout<<sum<<endl;

    return 0;
}