#include <bits/stdc++.h>   #define For(i, a, b) for(int i = a; i <= b; i++)   #define Ford(i, a, b) for(int i = a; i >= b; i--)   #define make_pair(a,b) mp(a, b)       using namespace std;   const int N= 2e5 + 1067, K = 17, md=1e9 + 7;   int n, k;   int f[N][30], g[1 << K], dem[30];   string s;      bool check(int x) {       int en = n - 1;       for(char j =  a ; j <  a  + k; j++) f[n][j] = f[n + 1][j] = n, dem[j] = 0;       Ford(i, n - 1, 0) {           for(char j =  a ; j <  a  + k; j++)                f[i][j] = f[i + 1][j];           ++dem[s[i]];           if (en >= i + x) {               --dem[s[en]];               en -= 1;           }           char c =  - ;           int diversity = 0;           for(char j =  a ; j <  a  + k; j++) {               if (dem[j]) {                   diversity += 1;                   c = j;               }           }           if (diversity == 0) {               for(char j =  a ; j <  a  + k; j++)                    f[i][j] = i + x - 1;           } else if (diversity == 1) {               f[i][c] = i + x - 1;           }       }              For(mask, 0, (1 << k) - 1) g[mask] = n;       g[0] = -1;       For(mask, 0, (1 << k) - 1) {           For(i, 0, k - 1) if (!(mask & (1 << i))) {               g[mask ^ (1 << i)] = min(g[mask ^ (1 << i)], f[g[mask] + 1][(char)( a  + i)]);            }       }              return g[(1 << k) - 1] < n;   }      int bs(int l, int r) {       while (l < r) {           if (l == r - 1) {               if (check(r))                    return r;               else                    return l;           }           int mid = (l + r) / 2;           if (check(mid))                l = mid;           else                r = mid - 1;       }       return l;   }       int main() {       ios_base::sync_with_stdio(false);       cin.tie(NULL);       cin >> n >> k;       cin >> s;       cout << bs(0, n) << endl;   }