There appear to be two recorded versions of Rav Nachman's story of the tainted grain.
In one, the king and the minister refuse to eat the tainted grain, and become the only sane ones in a word of mad people. In the other, the king and the minister both eat the tainted grain, but make marks on their foreheads to try to remember that they have become mad.
But here is an article containing a third version, where the king says to the minister: "I shall eat the tainted grain, and I shall join our people in their madness. You shall not: you will remain the only sane person in all the land. But there is one condition. You must leave the palace, you must wander as a beggar, and you must travel from town to town, from village to village. Everywhere you go, you must shout in all the marketplaces and from all the rooftops: Remember, my people, that you are mad!"
Can anyone help find the source of the third version?