The Great Telephone Robbery(1972)

Original title: שוד הטלפונים הגדול

Meshulam, a lowly bank clerk, has two hobbies: crime novels, and the ability to calculate investment interest in his head. When he learns of a local gang's plot to rob the bank, Meshulam realizes that this is his chance to make himself the hero of his own crime story -- by stopping them, in his own unique way!