#include<bits/stdc++.h>
using namespace std;
#define ll long long
int main()
{
    string s; cin>>s;
    ll n; cin>>n;
    string c1=""; ll ci1 = 0;
    string c2="";
    for(int i=0; i<s.size(); i++)
    {
        if(s[i]!='+')
        {
            c1+=s[i];
            ci1 = i;
        }
        else break;
    }

    for(int i=ci1+2; i<s.size(); i++)
    {
        if(s[i]!='+') c2+=s[i];

        else break;
    }
    reverse(c1.begin(), c1.end());
    reverse(c2.begin(), c2.end());

    ll x=0;
    ll y=0;
    for(int i=0; i<c1.size(); i++)
    {
        x+=(pow(10,i)*(c1[i]-'0'));
    }

    for(int i=0; i<c2.size(); i++)
    {
        y+=(pow(10,i)*(c2[i]-'0'));

    }

    //cout<<x<<" "<<y<<endl;

    ll diff = y-x;
    //cout<<diff<<endl;




    ll ex = x+ (n-1)*diff;
    //cout<<ex<<endl;


    ll t_sum = (ex*(ex+1))/2;
   //cout<<t_sum<<endl;

    ll fi_sum = ((x-1)*(x))/2;
    //cout<<fi_sum<<endl;
    ll sum = 0;

    ll pls=0;
    //cout<<x<<endl;
    for(int i=x+1; i<ex; i++)
    {
        pls++;
        if(pls%diff!=0)
        {
            sum+=i;
        }

    }

//    cout<<ex<<endl;

    cout<<t_sum-fi_sum-sum<<endl;

    return 0;
}