#include<bits/stdc++.h>
#define COGS
using namespace std;
const int maxlen=2010,maxk=210; 
char str[maxlen];
int a[maxlen],b[maxlen],k;
int temp,len1,len2,f[maxlen][maxlen];
inline void in(){
	#ifdef COGS
	freopen("blast.in","r",stdin);
	freopen("blast.out","w",stdout);
	#endif
	scanf("%s",str);len1=strlen(str);
	for (int i=1;i<=len1;i++){
		a[i]=str[i-1];
	}
	scanf("%s",str);len2=strlen(str);
	for (int i=1;i<=len2;i++){
		b[i]=str[i-1];
	}
	scanf("%d",&k); 
}
inline void dp(){
	int mlen=max(len1,len2);
	for (int i=1;i<=mlen;i++){
		f[0][i]=f[0][i-1]+k;
		f[i][0]=f[i-1][0]+k;
	}
	for (int i=1;i<=len1;i++){
		for (int j=1;j<=len2;j++){
			f[i][j]=f[i-1][j-1]+abs(a[i]-b[j]);
			temp=min(f[i][j-1],f[i-1][j]);
			temp+=k;
			f[i][j]=min(f[i][j],temp);
		}
	}
}
inline void p(){
	printf("%d",f[len1][len2]);
}
int Main(){
	in();
	dp();
	p();
	return 0;
}
int main(){;}
int xlm=Main();