#include <iostream>
#include <string>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <cmath>
#include <ctime>
#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <set>
#include <map>

#define maxlongint 2147483647
#define LL long long
#define pb push_back
#define mp make_pair

using namespace std;

char ch1[2010],ch2[2010];
int dp[2010][2010];
int k;

int main()
{
	freopen("blast.in","r",stdin);
	freopen("blast.out","w",stdout);
	ch1[0]='A',ch2[0]='A';
    scanf("%s",ch1+1);
    scanf("%s",ch2+1);
    scanf("%d",&k);
    int l1=strlen(ch1)-1,l2=strlen(ch2)-1;
    dp[0][0]=0;
	for(int i=1;i<=l1;i++)dp[i][0]=k*i;
	for(int i=1;i<=l2;i++)dp[0][i]=k*i;
    for(int i=1;i<=l1;i++)
        for(int j=1;j<=l2;j++)
            dp[i][j]=min(min(dp[i][j-1],dp[i-1][j])+k,dp[i-1][j-1]+abs(ch1[i]-ch2[j]));
    printf("%d\n",dp[l1][l2]);
    return 0;
}