https://cn.vjudge.net/problem/Gym-101982A
#include <iostream>
#include <cstring>
#include <queue>
#include <vector>
#include <algorithm>
#include <cstdio>
#include <set>
#include <map>
#include <cmath>
//#include<bits/stdc++.h>
using namespace std;
#define sfi(i) scanf("%d",&i)
#define sfs(i) scanf("%s",(i))
#define pri(i) printf("%d\n",i)
#define sff(i) scanf("%lf",&i)
#define ll long long
#define ull unsigned long long
#define mem(x,y) memset(x,y,sizeof(x))
#define INF 0x3f3f3f3f
#define eps 1e-3
#define PI acos(-1.0)
#define lowbit(x) ((x)&(-x))
#define fl() printf("flag\n")
#define MOD(x) ((x%mod)+mod)%mod
#define endl '\n'
#define pb push_back
#define FAST_IO ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
const int N=2e6+9;
const int M=4e5+9;
int main()
{
//FAST_IO;
//freopen("input.txt","r",stdin);
int k;
cin>>k;
string s,t;
cin>>s>>t;
int n=s.length();
int ans=0;
int num=0;
for(int i=0;i<n;i++)
{
if(s[i]==t[i])
{
num++;
}
}
if(num>=k)
{
ans=n-num+k;
}
else
{
ans=n-k+num;
}
cout<<ans<<endl;
return 0;
}