Your question is quite specific so I'll provide you with some directional information to help with your research. There are a number of helpful websites that offer instructional advice on the construction of paper airplanes in general. You should try searching on Google using keywords like ("paper airplanes" and "drinking straws"). Adding quotes around select phrases should provide you with more search results.
I've included two links below to help you get started. The first is from Instructables and it offers some clever designs. The second is a "Hoop Plane" from Exploratorium. I've seen this design before. 50 meters is a stretch but with some clever engineering, who knows. Good luck.
You'll have to experiment with several designs, including testing out different types of paper, before you achieve your goal of flying 50 meters. In order to maximize the length of flight achieved by your paper airplane you'll have to follow Bernoulli's principle and improve the aerodynamics of your plane. Education.com has a great section on building top-notch paper airplanes.