What was the energy input used to detonate the Hiroshima bomb?

It was a gun-type fission weapon. one piece of sub-critical material is shot into another.

Hiroshima bomb was accomplished by shooting a hollow cylinder of uranium over another hollow enriched uranium cylinder by means of four silk bags of cordite powder. It contained 64 kg (140 lb) of enriched uranium, of which less than a kilogram underwent nuclear fission.

The initial energy input was "four silk bags of cordite powder"

Wikipedia:

The Little Boy was 120 inches in length, 28 inches in diameter and weighed approximately 9,700 pounds. The design used the gun method to explosively force a hollow sub-critical mass of uranium-235 and a solid target cylinder together into a super-critical mass, initiating a nuclear chain reaction. This was accomplished by shooting one piece of the uranium onto the other by means of four cylindrical silk bags of slotted-tube cordite powder. The bomb contained 64 kg of enriched uranium. Most was enriched to 89% but some was only 50% uranium-235, for an average enrichment of 80%. of which less than a kilogram underwent nuclear fission, and of this mass only 0.6 g was transformed into a different type of energy; initially kinetic energy, then heat and light.

It was the Nagasaki bomb that used a lot of conventional explosive to detonate the physics package. The bomb was called the Fat Man because it was short and squat in order to house all that directed explosive.

The Pu in the physics package was brought to critical mass (where the rapid chain reaction is sustained) by using directed conventional implosion to crunch two hemispheres of plutonium into a small solid ball.[http://en.wikipedia.org/wiki/Fat_Man#Interior_of_b...