Neba naranai ねばならない

 Predicative phrase (expressing obligation) meaning: have to, must. 

1. After the stem of nai-form of verb 

もう行かねばなりません。 

Mou ikaneba narimasen. 

I have to leave now. 

若いうちはもっと仕事せねばなりません。 

Wakai uchi wa motto shigoto seneba narimasen. 

You must work harder while you are young. 

(this uses the antiquated form se[neba] instead of the more common stem shi)

-> See also: nakereba naranai