#include<bits/stdc++.h>

using namespace std;

int k,f[2100][2100];
string a,b;

int main()
{
	freopen("blast.in","r",stdin);
	freopen("blast.out","w",stdout);
	cin>>a>>b>>k;
	f[0][0]=0;
	for(int i=1;i<2100;i++)
	{
		f[i][0]=i*k;
		f[0][i]=i*k;
	}
	//cout<<f[0][0];
	for(int i=1;i<=a.size();i++)
	 for(int j=1;j<=b.size();j++)
	 {
	 	//if(i==0) continue
	 	f[i][j]=min(f[i-1][j-1]+abs((int)a[i-1]-(int)b[j-1]),min(f[i-1][j]+k,f[i][j-1]+k));
	 	//cout<<f[i][j]<<endl;
	 }
	cout<<f[a.size()][b.size()];
	return 0;
}