/*胡金梁*/
#include<bits/stdc++.h>
using namespace std;
#define __MY_TEST__ 0
#define int long long
const int mod1=1e9+7,mod2=998244353;
signed main(){
#if __MY_TEST__
	freopen(".in","r",stdin);
	freopen(".out","w",stdout);
#endif
	ios::sync_with_stdio(0);
	cin.tie(0);cout.tie(0);
	int n,ans=0;
	string s,t;
	cin>>n>>s>>t;
	set<int>st1,st2;
	for(int i=0;i<n;i++)
	{
		int p=0,hash1=0,hash2=0;
		for(int j=i;j<n;j++)
		{
			while(p<n&&s[p]!=t[j])
			{
				p++;
			}
			if(p>=n) break;
			p++;
			ans++;
			hash1=hash1*27+t[j]-'a'+1;
			hash1%=mod1;
			hash2=hash2*27+t[j]-'a'+1;
			hash2%=mod2;
			if(st1.count(hash1)&&st2.count(hash2))
			{
				ans--;
			}
			st1.insert(hash1);
			st2.insert(hash2);
		}
	}
	cout<<ans<<endl;
#if __MY_TEST__
	fclose(stdin);
	fclose(stdout);
#endif
}