#include <bits/stdc++.h>   const int M = 1 << 20, L = 100020;   char s[L];   int n, m, g[M], f[M], i, j, k, x, y, D;   void init() {     scanf( %d%d%s , &n, &m, s + 1);     D = (1 << m) - 1;     for (i = 1; i < n; i++) {       x = s[i] - 97;       y = s[i + 1] - 97;       if (x != y) g[1 << x | 1 << y]++;     }     for (j = 0; j < m; j++)       for (i = 0; i <= D; i++)         if (i >> j & 1) g[i] += g[i ^ 1 << j];   }   int min(int x, int y) { return x < y ? x : y; }   void work() {     memset(f, 0x3f, sizeof(f));     f[0] = 0;     for (i = 0; i <= D; i++)       for (j = 0; j < m; j++)         if ((i >> j & 1) == 0)           f[i | 1 << j] = min(f[i | 1 << j], f[i] + g[D] - g[i] - g[D ^ i]);     printf( %d , f[D]);   }   int main() {     init();     work();     return 0;   }   