#include<iostream>
#include<string>
using namespace std;
int main(){
	int n;
	cin>>n;
	string s;
	cin>>s;
	string t;
	cin>>t;
	int count=0;
	for(int i=0;i<s.length();){
		for(int j=0;j<t.length();){
			if(s[i]==t[j]){
				i++;
				j++;
			}
			else{
				count++;
				i++;
				j++;
			}
		}
	}
	cout<<count;
}