#include<bits/stdc++.h>
using namespace std;
const int N=103;
int k,n,m,f1[N][N][N],f2[N][N][N],f3[N][N][N],f4[N][N][N],g[N][N],mc[N][N];
char a[N],b[N];
inline void U(int &x,int y){
	if(x>y)x=y;
}
int main(){
	scanf("%d",&k);
	scanf("%s%s",a+1,b+1);
	n=strlen(a+1),m=strlen(b+1);
	memset(f1,0x3f,sizeof(f1));
	memset(f2,0x3f,sizeof(f2));
	memset(f3,0x3f,sizeof(f3));
	memset(f4,0x3f,sizeof(f4));
	memset(g,0x3f,sizeof(g));
	for(int i=1;i<=n;++i)for(int j=1;j<=m;++j){
		mc[i][j]=0;
		while(i+mc[i][j]<=n&&j+mc[i][j]<=m&&a[i+mc[i][j]]==b[j+mc[i][j]])++mc[i][j];
	}
	f1[0][0][k]=f2[0][0][k]=0;
	for(int i=0;i<=n;++i)for(int j=0;j<=m;++j){
		int v=mc[i+1][j+1],w=g[i][j];
		if(a[i+1]==b[j+1])U(g[i+1][j+1],w+1);
		U(f3[i+1][j][k],w+1);
		U(f4[i][j+1][k],w+1);
		for(int l=1;l<=k;++l){
			int &w1=f1[i][j][l],&w2=f2[i][j][l],&w3=f3[i][j][l],&w4=f4[i][j][l];
			if(v>=l){
				if(l==k)U(g[i+l][j+l],w1+l),U(g[i+l][j+l],w2+l);
				else U(f3[i+l][j+l][k-l],w1+l),U(f4[i+l][j+l][k-l],w2+l);
			}else{
				U(w2,w3);
				U(w1,w4);
			}
			if(l==1){
				U(f3[i+1][j][k],w1+1),U(f4[i][j+1][k],w2+1);
				if(a[i+1]==b[j+1])U(g[i+1][j+1],w3+1),U(g[i+1][j+1],w4+1);
			}else{
				U(f1[i+1][j][l-1],w1+1),U(f2[i][j+1][l-1],w2+1);
				if(a[i+1]==b[j+1])U(f3[i+1][j+1][l-1],w3+1),U(f4[i+1][j+1][l-1],w4+1);
			}
			if(l==k)U(f3[i+1][j][l],w3+1),U(f4[i][j+1][l],w4+1);
		}
	}
	printf("%d\n",min({g[n][m],f1[n][m][k],f2[n][m][k],f3[n][m][k],f4[n][m][k]}));
	return 0;
}