#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, k, pg, pt;
  scanf("%d %d", &n, &k);
  char a[105];
  scanf("%s", a);
  for (int i = 0; i < n; i++) {
    if (a[i] == 'G') pg = i;
    if (a[i] == 'T') pt = i;
  }
  int x = abs(pg - pt);
  if (x % k == 0) {
    int fg = 0, st, ed;
    if (pg < pt) {
      st = pg;
      ed = pt + 1;
    } else {
      st = pt;
      ed = pg + 1;
    }
    for (int i = st; i < ed; i++) {
      if (a[i] == '#') {
        int xx = abs(pg - i);
        if (xx % k == 0) {
          fg = 1;
          break;
        }
      }
    }
    if (fg == 1)
      printf("NO\n");
    else
      printf("YES\n");
  } else
    printf("NO\n");
  return 0;
}
