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

int main(){
    string s;
    cin >> s;
    ll n;
    cin >> n;

    vector<int>a,b,c;

    for(int i=0; i<s.size(); i++){
        if(i%2==0){
            a.push_back(s[i]-'0');
        }
    }

    ll diff= a[1]-a[0];
    ll sum= a[0];
    ll num= a[0];

    for(int i=0; i<n-1; i++){
        num += diff;
        sum+=num;
    }

    cout<< sum <<endl;



}