### Instruction:
Who has won the most grand slams in men's singles tennis in open era?

### Input:
The Open Era is the current era of professional tennis. It began in 1968 when the Grand Slam tournaments allowed professional players to compete with amateurs, ending the division that had persisted since the dawn of the sport in the 19th century. The first open tournament was the 1968 British Hard Court Championships held in April, followed by the inaugural open Grand Slam tournament, the 1968 French Open, a month later. Unless otherwise sourced, all records are based on data from the Association of Tennis Professionals (ATP), the International Tennis Federation (ITF), and the official websites of the four Grand Slam tournaments. All rankings-related records are based on ATP rankings, which began in 1973.

### Response:
Rafael Nadal and Novak Djokovic won 22 times.