eps = 10e-10
n = 0
a = -1^n*(1/(6*n+1)+1/(6*n+5))
pi = 3.1415926535897932384626433832795
s = a
t1 = Time
do while abs(a) > eps
 n = n + 1
 a = -1^n*(1/(6*n+1)+1/(6*n+5))
 s = s + a
Loop
t2= Time
dt=FormatDateTime(t2-t1)
r_pi=s*3
msgbox "Esp="& eps & vblf & "Ист. Pi=" & pi & vblf & "Расч. Pi=" & r_pi & vbLf & "n=" & n & vblf & "dt=" & dt,vbok,"Лаба"