Risk of Ruin – Doomed to Failure

I am new to trading, and after some backtest, I was trying to calculate the risk of Ruin. The formula goes like:

R=[(1-A)/(1+A)]^c

R: probability of Ruin A:The difference between the percentages of wining trades and the percentage of losing trades. c: the number of trades in a account

Now it seems that by using that formula, if you have a winning percentage below 50% you are always doomed to failure, am I correct? I'm using a trading system with about just 20% winning rate but a R/R of at least 12, sometimes going to 50…