C++ :

#include <bits/stdc++.h>
using namespace std;
string a,b;
long long k,sum,cnt;
int main() {
//  freopen("magic.in","r",stdin);
//  freopen("magic.out","w",stdout);
    cin>>a>>b>>k;
    int lena=a.size();
    for(int i=0;i<lena;i++){
        if(a[i]==b[i]) cnt++;
        else break;
    }
    sum=lena-cnt;
//  cout<<a.size()<<" "<<sum<<endl; 
    for(int i=cnt+1;i<lena;i++){
        if(b[i]=='0') sum+=1;
        else sum+=2;
    }
    cout<<sum*k;
    return 0;
}