Who Looks for Gold? (1974)

Original title: Kdo hledá zlaté dno

When he returns to Prague from a stint in the Army, Lada does not seem to fit in anywhere, and he cannot get the hang of the system of deliberately underperforming on the job. His girlfriend tries to keep him in the city with a variety of stratagems, but he eventually takes a job as a truck driver on a dam-building project. He uses the truck to visit his girl on weekends. Ingenuous, he is unaware that the truck is being used for black-market smuggling, and that his girlfriend two-times on him when he cannot arrange to leave on time for his weekend.