A sample of radioactive material decays simultaneouly by two processes A and B with half-lives `(1)/(2)` and `(1)/(4)h`, respectively. For the first half hour it decays with the process A, next one hour with the proecess B, and for further half an hour with both A and B. If, origianlly, there were `N_0` nuceli, find the number of nuclei after 2 h of such decay.