#include<fstream>
#include<string>
#include<cmath>
#include<cstdlib>
#include<cstring>
using namespace std;
ifstream fin("blast.in");
ofstream fout("blast.out");
int K;
char a[2001],b[2001];
string A,B;
int f[2001][2001];
int min(int a,int b,int c)
{
	int temp;
	if(a>b) temp=b; else temp=a;
	if(temp>c) return c;else return temp;
}
int main()
{
	int LA,LB;
	fin>>A>>B>>K;
	LA=A.length();LB=B.length();
	int i,j;
	int temp=0;
	for(i=1;i<=LA;i++)
	{
		f[i][0]=i*K;
		a[i]=A[i-1];
	}
	for(i=1;i<=LB;i++)
	{
		f[0][i]=i*K;
		b[i]=B[i-1];
	}
	for(i=1;i<=LA;i++)
		for(j=1;j<=LB;j++)
		{
				f[i][j]=min(f[i-1][j]+K,f[i][j-1]+K,f[i-1][j-1]+abs(int(a[i])-int(b[j])));
		}
	fout<<f[LA][LB]<<endl;
	return 0;
}