#include <bits/stdc++.h>
using namespace std;
char s1[2110], s2[2110];
int f[2110][2110];
 
int main()
{
    int n1, n2, K;
    scanf("%s", s1 + 1); n1 = strlen(s1 + 1);
    scanf("%s", s2 + 1); n2 = strlen(s2 + 1);
    scanf("%d", &K);
    memset(f, 63, sizeof(f));
    for(int i = 1; i <= n1; i++) f[i][0] = i * K;
    for(int i = 1; i <= n2; i++) f[0][i] = i * K;
    f[0][0] = 0;
     
    for(int i = 1; i <= n1; i++)
        for(int j = 1; j <= n2; j++)
        {
            f[i][j] = min(f[i][j - 1] + K, f[i - 1][j] + K);
            f[i][j] = min(f[i][j], f[i - 1][j - 1] + abs(s1[i] - s2[j]));
        }
     
    printf("%d\n", f[n1][n2]); 
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
char s1[2110],s2[2110];
int f[2110][2110];
 
int main()
{
    int n1,n2,K;
    scanf("%s",s1+1);n1=strlen(s1+1);
    scanf("%s",s2+1);n2=strlen(s2+1);
    scanf("%d",&K);
    memset(f,63,sizeof(f));
    for(int i=1;i<=n1;i++)f[i][0]=i*K;
    for(int i=1;i<=n2;i++)f[0][i]=i*K;
    f[0][0]=0;
     
    for(int i=1; i<=n1;i++)
        for(int j=1;j<=n2;j++)
        {
            f[i][j]=min(f[i][j-1]+K,f[i-1][j]+K);
            f[i][j]=min(f[i][j],f[i-1][j-1]+abs(s1[i]-s2[j]));
        }
     
    printf("%d\n",f[n1][n2]); 
    return 0;
}