#include <bits/stdc++.h>   using namespace std;   #pragma comment(linker,  /STACK:60777216 )   const int N = 1111111;   char s[N];   int n, k;   const int mod = 1000000007;   int f[N], g[N], h[N], ps[N], pW[N], pX[N], pB[N], p2[N], pr[N];   inline void solve(int *f, int *g, char W, char B, char X) {     pW[0] = pX[0] = pB[0] = 0;     if (s[0] == W)       pW[0] = 1;     else if (s[0] == B)       pB[0] = 1;     else if (s[0] == X)       pX[0] = 1;     for (int i = 1; i < n; ++i) {       pW[i] = pW[i - 1];       pB[i] = pB[i - 1];       pX[i] = pX[i - 1];       if (s[i] == W)         pW[i]++;       else if (s[i] == B)         pB[i]++;       else if (s[i] == X)         pX[i]++;     }     f[0] = 0;     g[0] = 0;     if (k == 1) {       if (s[0] == W || s[0] == X) {         f[0]++;       }       if (s[0] == B || s[0] == X) {         g[0]++;       }     } else {       g[0]++;       if (s[0] == X) g[0]++;     }     ps[0] = 0;     if (s[0] == X) ps[0] = 1;     int lb = -1;     if (s[0] == B) lb = 0;     for (int i = 1; i < n; ++i) {       if (i >= k - 1) {         int cW = pW[i];         if (i > k - 1) cW -= pW[i - k];         int cB = pB[i];         if (i > k - 1) cB -= pB[i - k];         int cX = pX[i];         if (i > k - 1) cX -= pX[i - k];         if (cB == 0) {           if (i == k - 1)             f[i] = 1;           else {             if (s[i - k] == B) {               f[i] = g[i - k];             } else if (s[i - k] == W) {               f[i] = 0;             } else {               if (i == k)                 f[i] = 1;               else                 f[i] = g[i - k - 1];             }           }         } else           f[i] = 0;         g[i] = 0;         if (s[i] == B || s[i] == X) g[i] += g[i - 1];         if (s[i] == W || s[i] == X) {           if (cB) {             g[i] += ps[i - 1];             if (g[i] >= mod) g[i] -= mod;             g[i] += mod - ps[lb];             if (g[i] >= mod) g[i] -= mod;             g[i] += g[lb];             if (g[i] >= mod) g[i] -= mod;           } else {             g[i] += ps[i - 1];             if (g[i] >= mod) g[i] -= mod;             if (i >= k) {               g[i] += mod - ps[i - k];               if (g[i] >= mod) g[i] -= mod;             }           }         }       } else {         f[i] = 0;         g[i] = p2[pX[i]];       }       ps[i] = ps[i - 1];       if (s[i] ==  X ) ps[i] += g[i - 1];       if (ps[i] >= mod) ps[i] -= mod;       if (s[i] == B) lb = i;     }   }   inline long long solution() {     solve(f, h,  B ,  W ,  X );     reverse(s, s + n);     solve(g, h,  W ,  B ,  X );     reverse(g, g + n);     reverse(s, s + n);     pX[0] = 0;     if (s[0] ==  X ) pX[0] = 1;     for (int i = 1; i < n; ++i) {       pX[i] = pX[i - 1];       if (s[i] ==  X ) pX[i]++;     }     for (int i = 1; i < n; ++i) {       g[i] = ((long long)g[i] * p2[pX[i - 1]]) % mod;     }     ps[n - 1] = g[n - 1];     for (int i = n - 2; i >= 0; --i) {       ps[i] = ps[i + 1] + g[i];       if (ps[i] >= mod) ps[i] -= mod;     }     int ans = 0;     for (int i = 0; i < n; ++i) {       int cur = ((long long)f[i] * ps[i + 1]) % mod;       cur = ((long long)cur * pr[pX[i]]) % mod;       ans = (ans + cur) % mod;     }     return ans;   }   int main() {     gets(s);     sscanf(s,  %d%d , &n, &k);     gets(s);     p2[0] = 1;     for (int i = 1; i <= n; ++i) {       p2[i] = p2[i - 1] * 2;       if (p2[i] >= mod) p2[i] -= mod;     }     pr[0] = 1;     pr[1] = mod / 2 + 1;     for (int i = 2; i <= n; ++i) pr[i] = ((long long)pr[i - 1] * pr[1]) % mod;     cout << solution() << endl;   }