"...THISISTHEEND"

A random generator emits letters based on the English letter frequencies as given below: Out of 10000 letters, it would emit 1203 E's, 910 T's, 812 A's, 768 O's, 731 I's 695 N's, 628 S's 602 R's, 592 H's, 432 D's, 398 L's, 288 U's, 271 C's, 261 M's, 230 F's, 211 Y's, 209 W's, 203 G's, 182 P's, 149 B's, 111 V's, 69 K's, 17 X's, 11 Q's, 10 J's, and 7 Z's. The generated letters are concatenated to a string starting from an empty string. What is the probability that we would see a "...THISISTHEEND" before seeing any "...THIS...", "...IS...", "...THE...", or "...END..."? Answer format: N/D (irreducible fraction) Check point: Answer=1/245 to see a "...THEEND" before seeing any "...THE..." or "...END..." if it were to emit E,T,N,H,D with equal probabilities