//qoj3680
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

const int N = 1e6 + 10;
const ll P = 1e9 + 7;
int n, k;
ll f[N], g[N], F[N], G[N];
char s[N];

#define cl(x) ((x) == 'X' ? 2 : 1)

int main(){
	scanf("%d%d", &n, &k);
	scanf("%s", s+1);
	f[0] = g[n+1] = 1;
	for(int i = 1, la = 0; i <= n; ++ i){
		if(s[i] == 'W'){
			la = i;
		}
		if(la >= i - k + 1){
			f[i] = f[i-1] * cl(s[i]) % P;
		} else {
			int v = s[i-k] == 'B' ? 0 : i==k ? 1 : f[i-k-1];
			f[i] = (P + f[i-1] * cl(s[i]) - v) % P;
		}
	}
	for(int i = n; i >= 1; -- i){
		f[i] = s[i] == 'B' ? 0 : f[i-1];
	}
	for(int i = 1, la = 0; i <= n; ++ i){
		if(s[i] == 'W'){
			la = i;
		}
		if(la < i - k + 1){
			F[i] = f[i-k];
		}
	}
	for(int i = n, la = n+1; i >= 1; -- i){
		if(s[i] == 'B'){
			la = i;
		}
		if(la <= i + k - 1){
			g[i] = g[i+1] * cl(s[i]) % P;
		} else {
			int v = s[i+k] == 'W' ? 0 : n-i+1==k ? 1 : g[i+k+1];
			g[i] = (P + g[i+1] * cl(s[i]) - v) % P;
		}
	}
	for(int i = 1; i <= n; ++ i){
		g[i] = s[i] == 'W' ? 0 : g[i+1];
	}
	for(int i = n, la = n+1; i >= 1; -- i){
		if(s[i] == 'B'){
			la = i;
		}
		if(la > i + k - 1){
			G[i] = g[i+k];
		}
	}
	ll ans = 0, sum = 0;
	for(int i = 1; i <= n; ++ i){
		sum = (sum * cl(s[i]) + F[i]) % P;
		ans = (ans + sum * G[i+1]) % P;
	}
	printf("%lld\n", ans);
	return 0;
}