using namespace std;
string A,B;
int g[2010][2010]; 
int k;
int xiao(int a,int b,int c)
{
	int d;
    d=min(a,b);
    if(d<c) return d;
      else return c;
    
}

int jueduizhi(int a,int b)
{
	int c;
	if(a>=b) {c=a-b;} 
	else c=b-a; 
	return c;
}
int main()
{  
 //  freopen("blast.in","r",stdin);
//   freopen("blast.out","w",stdout);   
   cin>>A;
   cin>>B;
   cin>>k;
 //g[0][0]=0;
   int la=A.length();
   int lb=B.length();
       for(int i=1;i<=la;i++)
	       for(int j=1;j<=lb;j++) 
		       {
				g[0][j]=j*k;   
                g[i][0]=i*k;
                int f;
                f=jueduizhi(A[i-1],B[j-1]);
                g[i][j]=xiao(g[i-1][j]+k, g[i][j-1]+k, g[i-1][j-1]+f);
                }
                
				cout<<g[la][lb];
                
  
}