Problem: You are given a string s of length n. Each character is either one of the first k lowercase Latin letters or a question mark.

You are asked to replace every question mark with one of the first k lowercase Latin letters in such a way that the following value is maximized.

Let f_i be the maximum length substring of string s, which consists entirely of the i-th Latin letter. A substring of a string is a contiguous subsequence of that string. If the i-th letter doesn't appear in a string, then f_i is equal to 0.

The value of a string s is the minimum value among f_i for all i from 1 to k.

What is the maximum value the string can have?

Input

The first line contains two integers n and k (1 ≤ n ≤ 2 ⋅ 10^5; 1 ≤ k ≤ 17) — the length of the string and the number of first Latin letters used.

The second line contains a string s, consisting of n characters. Each character is either one of the first k lowercase Latin letters or a question mark.

Output

Print a single integer — the maximum value of the string after every question mark is replaced with one of the first k lowercase Latin letters.

Examples

Input


10 2
a??ab????b


Output


4


Input


9 4
?????????


Output


2


Input


2 3
??


Output


0


Input


15 3
??b?babbc??b?aa


Output


3


Input


4 4
cabd


Output


1

Note

In the first example the question marks can be replaced in the following way: "aaaababbbb". f_1 = 4, f_2 = 4, thus the answer is 4. Replacing it like this is also possible: "aaaabbbbbb". That way f_1 = 4, f_2 = 6, however, the minimum of them is still 4.

In the second example one of the possible strings is "aabbccdda".

In the third example at least one letter won't appear in the string, thus, the minimum of values f_i is always 0.

Solution (in CPP):

Solution:
#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define SZ(x) ((int)x.size())
#define lowbit(x) x&-x
#define pb push_back
#define ALL(x) (x).begin(),(x).end()
#define UNI(x) sort(ALL(x)),x.resize(unique(ALL(x))-x.begin())
#define GETPOS(c,x) (lower_bound(ALL(c),x)-c.begin())
#define LEN(x) strlen(x)
#define MS0(x) memset((x),0,sizeof((x)))
#define Rint register int
#define ls (u<<1)
#define rs (u<<1|1)
typedef unsigned int unit;
typedef long long ll;
typedef unsigned long long ull;
typedef double db;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef vector<int> Vi;
typedef vector<ll> Vll;
typedef vector<pii> Vpii;
template<class T> void _R(T &x) { cin >> x; }
void _R(int &x) { scanf("%d", &x); }
void _R(ll &x) { scanf("%lld", &x); }
void _R(ull &x) { scanf("%llu", &x); }
void _R(double &x) { scanf("%lf", &x); }
void _R(char &x) { scanf(" %c", &x); }
void _R(char *x) { scanf("%s", x); }
void R() {}
template<class T, class... U> void R(T &head, U &... tail) { _R(head); R(tail...); }
template<class T> void _W(const T &x) { cout << x; }
void _W(const int &x) { printf("%d", x); }
void _W(const ll &x) { printf("%lld", x); }
void _W(const double &x) { printf("%.16f", x); }
void _W(const char &x) { putchar(x); }
void _W(const char *x) { printf("%s", x); }
template<class T,class U> void _W(const pair<T,U> &x) {_W(x.fi);putchar(' '); _W(x.se);}
template<class T> void _W(const vector<T> &x) { for (auto i = x.begin(); i != x.end(); _W(*i++)) if (i != x.cbegin()) putchar(' '); }
void W() {}
template<class T, class... U> void W(const T &head, const U &... tail) { _W(head); putchar(sizeof...(tail) ? ' ' : '\n'); W(tail...); }
const int MOD=1e9+7,mod=998244353;
ll qpow(ll a,ll b) {ll res=1;a%=MOD; assert(b>=0); for(;b;b>>=1){if(b&1)res=res*a%MOD;a=a*a%MOD;}return res;}
const int MAXN=4e5+10,MAXM=1e7+10;
const int INF=INT_MAX,SINF=0x3f3f3f3f;
const ll llINF=LLONG_MAX;
const int inv2=(MOD+1)/2;
const int Lim=1<<20;

int n,k;
char s[MAXN];
int nxt[MAXN][20],sum[MAXN][20];
int mx[30];
Vll vec[MAXN];

bool chk(int m)
{
    for(int j=0;j<k;j++)nxt[n+1][j]=nxt[n+2][j]=n+2;
    for(int i=n;i;i--)
        for(int j=0;j<k;j++)
        {
            if(sum[i+m-1][j]-sum[i-1][j]==m)
            nxt[i][j]=i+m;
            else nxt[i][j]=nxt[i+1][j];
        }
    Vi dp((1<<k),n+2);
    dp[0]=1;
    for(int s=0;s<(1<<k);s++)
        for(int i=0;i<k;i++)if(!(s&(1<<i)))
        {
            dp[s|(1<<i)]=min(dp[s|(1<<i)],nxt[dp[s]][i]);
        }
    return dp.back()<=n+1;
}

void solve()
{
    R(n,k);
    scanf("%s",s+1);
    for(int i=1;i<=n;i++)
    {
        for(int j=0;j<k;j++)
        {
            sum[i][j]=sum[i-1][j]+(s[i]=='a'+j)+(s[i]=='?');
        }
    }
    int l=1,r=n,res=0;
    while(l<=r)
    {
        int mid=(l+r)/2;
        if(chk(mid))l=mid+1,res=mid;
        else r=mid-1;
    }
    W(res);
}

int main()
{
    int T=1;
    //scanf("%d",&T);
    for(int kase=1;kase<=T;kase++)
    {
        //printf("Case #%d: ",kase);
        solve();
    }
    return 0;
}