#include <bits/stdc++.h>
#define ll long long
using namespace std;
ll n,m,a[500005],b[500050],mn,q,ans,r,l,c,sum,h,k,p,x,y,vis[55][55];
const int N=100005;
map<char,ll>mp,mpp;
string s,t;
bool f;
int main()
{
    ios_base::sync_with_stdio(NULL);cin.tie(0);cout.tie(0);
 
    cin>>n>>m;
    cin>>s>>t;
    for(int i=0;i<m;i++)
        mp[t[i]]++;
 
    for(int r=0;r<n;r++)
    {
        mpp[s[r]]++;
 
        while(mpp[s[r]]>mp[s[r]])
            mpp[s[l]]--,l++;
 
        ans+=(r-l+1);
    }
 
    cout<<ans<<endl;
}

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NCAzCmFhYWIKYWJhCg==

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