#include <cstdio>
#include <cstring>

using namespace std;

#define DIST(X,Y) (int)(((X)-(Y))>=0?((X)-(Y)):((Y)-(X)))

inline int MIN (int a, int b, int c)
{
	if (a <= b)
		return c <= a ? c : a;
	else
		return c <= b ? c : b;
}

int dym[2010][2010];

int main ()
{
	freopen("blast.in", "r", stdin);
	freopen("blast.out", "w", stdout);
	
	char s1[2010], s2[2010];
	scanf("%s", s1);
	scanf("%s", s2);
	
	int l1 = strlen(s1), l2 = strlen(s2), K;
	scanf("%d", &K);
	
	for (int i=1; i<=l1 || i<=l2; i++)
		dym[0][i] = dym[i][0] = K*i;
	
	for (int i=1; i<=l1; i++)
		for (int j=1; j<=l2; j++)
			dym[i][j] = MIN(dym[i-1][j-1]+DIST(s1[i-1],s2[j-1]),
							dym[i-1][j]+K, dym[i][j-1]+K);
	
	printf("%d\n", dym[l1][l2]);
	
	return 0;
}