In the first month he can run 3 miles.
In the second month he can run 6 miles because 3 x 2 = <<3*2=6>>6
In the third month he can run 12 miles because 6 x 2 = <<6*2=12>>12
In fourth month he can run 24 miles because 12 x 2 = <<12*2=24>>24
In fifth month he can run 48 miles because 24 x 2 = <<24*2=48>>48
He needs to start training 5 months ahead of time because 24 < 26.3 and 48>26.3.
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