Output from rrdtool has both expected and not expected.

output contains following both lines, expected and not expected

1. " 1427533200: -nan -nan -nan " --> which is not expected and need code to vomit these lines from the output of rrdtool

2. " 1427532900: 3.2684113920e+09 9.2589260800e+08 4.1943040000e+09 "

Please help me how to vomit / skip lines which contains "-nan -nan -nan" from the output of rrdtoold and proced only with correct data