c montecarlo method pi
        write(6,*) 'n?' 
        read(5,*) ntrial
        write(6,*) 'randseed?'
        read(5,*) iseed
      open(unit = 10, status ='new', file = 'output.txt',
     $  form = 'formatted')
        nin=0
        do 10 i=1,ntrial
          x=ran(iseed)*2.0-1.0
          y=ran(iseed)*2.0-1.0
          r=x**2+y**2
          if(r.le.1) nin=nin+1
          pi=(float(nin)/float(i))*4
          sa=pi-3.14159265
          write(10,*) i,'   ',pi
   10   continue

 9999   stop
        end

        function iran(iseed)
        iseed=iseed*48828125
        if(iseed.le.0) iseed=(iseed+2147483647)+1
        iran=iseed
        return
        end

        function ran(iseed)
        iseed=iseed*48828125
        if(iseed.le.0) iseed=(iseed+2147483647)+1
        ran=float(iseed)/2147483647
        return
        end