#include<bits/stdc++.h>
using namespace std;

//#define debug(...)   printf( __VA_ARGS__ )
#define debug(...)   /****nothing****/

#define ll long long
#define ull unsigned long long
#define pb push_back
#define mem(arr,val)    memset(arr,val,sizeof(arr))
#define mp make_pair
#define pii pair<int,int>
#define F first
#define S second
#define sz(x) (int)(x).size()
#define nopos string::npos
#define fr(i,a,b) for(i=a;i<=b;i++)
#define frn(i,a,b) for(i=a;i>=b;i--)


int n,sz,cnt,i,j;
set<char> data;
char str[123456];

int main()
{

    while(cin>>n)
    {
        scanf("%s",str+1);

        int ans=n+1;
        data.clear();

        for(i=1;i<=n;i++)
            data.insert(str[i]);

        cnt=data.size(); // all types of pokemon in string str

        for(i=1;i<=n;i++)
        {
            int low=i-1 , high=n+1;
            while(high-low>1)
            {
                int mid=(high+low)/2;
                data.clear();

                for(j=i;j<=mid;j++)
                  data.insert(str[j]);  //to evaluate : how many distinct character from i index to mid index

                if(data.size()>=cnt)
                    high=mid;
                else
                  low=mid;
            }

            if(high!=n+1) // we got a segment from i to high where number of distinct characters are equal to cnt
             {
                 ans=min(ans,high-i+1);
             }
        }

        cout<<ans<<'\n';

    }



    return 0;
}