First of all, as the others said, 50kg is way too little for that height. Even if it is not 100% efficient, try to check your BMI. You can use a calculator like this
BMI calculator | Check your BMI The BMI will tell you if the weight you want is healthy or not since the body needs a specific number of calories to survive, to use the basic functions
Second of all, don't starve yourself, please. Start with smaller goals, start with 5kg for example, not 20kg, this goal is very unrealistic. You will gain everything back when you start eating a bit more. You can try to reduce a little bit the number of calories and maybe include a little bit of sport. This is a healthy way of losing weight. If you starve yourself, your body is going in survival mode and stocks even more what you're eating, so it is really not healthy. Plus, the scale is not everything. I didn't lose any weight in years, but the shape of my body changed because of exercise and cleaner eating.
I'm sorry I wrote so much, but if you'd like even more details about these things, I can tell you more stuff. Just please don't starve yourself like this, it's not healthy, it's not pleasant and it will NOT provide the results you want.