#include <iostream>#include <cstdio>#include <cmath>#include <cstring>using namespace std;double dp[2][20][20];int pre, now;int n;int main(){while (scanf("%d", &n) != EOF){int i, j;pre = 0;now = 1;char a[20];int w = 0, k = 0;memset(dp, 0, sizeof(dp));dp[pre][n][0] = 1;while (scanf("%s", a) != EOF){if (strcmp(a, "End") == 0)break;for (i = 0; i <= n; i++){j = n - i;if (a[0] == 'W'){if (w >= n) break;if (i > 0)dp[now][i - 1][j + 1] += dp[pre][i][j] * i/(n - w);dp[now][i][j] += dp[pre][i][j] * (j - w)/(n - w);}else if (a[0] == 'K'){if (k >= n) break;if (j > 0)dp[now][i + 1][j - 1] += dp[pre][i][j] * j/(n - k);dp[now][i][j] += dp[pre][i][j] * (i - k)/(n - k);}}if (i != n + 1)memcpy(dp[now], dp[pre], sizeof(dp[0]));if (a[0] == 'W'){w++;k = 0;}else{k++;w = 0;}int m = pre;pre = now;now = m;memset(dp[now], 0, sizeof(dp[now]));}printf("%.2fn", dp[pre][n][0]);}return 0;}
