134277/(1.25)^4 = 54999.8592 (exactly) so I assume S1 = $55,000.
It's kind of strange to phrase things in terms of this S1 value when they say nobody makes below S2. I guess the idea is that if they introduce lower levels they didn't want to force themselves into negative numbers.
The other baseline number they mention is E3 (the baseline equity) which is approximately equal to S3 = S1 * (1.25)^2 ~ $86k.