Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Pick # | NFL Team | Player | Position | College |
| --- | --- | --- | --- | --- |
| 417 | Buffalo Bills | Wayne Lineberry | Linebacker | East Carolina |
| 418 | Atlanta Falcons | Paul Williams | Running back | California |
| 419 | Philadelphia Eagles | Bob Haack | Tackle | Linfield (Ore.) |
| 420 | Pittsburgh Steelers | Bill Eppright | Kicker | Kent State |
| 421 | Cincinnati Bengals | Terry Story | Tackle | Georgia Tech |
| 422 | Boston Patriots | George Muse | Linebacker | Grambling |
| 423 | New Orleans Saints | Chico Kurzawski | Defensive back | Northwestern |
| 424 | Detroit Lions | Gary Steele | Tight end | Army |
| 425 | Denver Broncos | Buster O'Brien | Quarterback | Richmond |
| 426 | Washington Redskins | Rich Dobbert | Defensive end | Springfield (Mass.) |
| 427 | Miami Dolphins | Tom Krallman | Defensive end | Xavier |
| 428 | Green Bay Packers | John Mack | Running back | Central Missouri |
| 429 | New York Giants | Ken Riley | Linebacker | Texas-Arlington |
| 430 | Houston Oilers | Hank Autry | Center | Southern Mississippi |
| 431 | Chicago Bears | Bob Long | Wide receiver | Texas A&M |
| 432 | San Francisco 49ers | Joe Rushing | Linebacker | Memphis State |
| 433 | Minnesota Vikings | Wendell Housely | Running back | Texas A&M |
| 434 | San Diego Chargers | Larry Rentz | Defensive back | Florida |
| 435 | St. Louis Cardinals | George Hummer | Center | Arizona State |
| 436 | Cleveland Browns | Bob Oliver | Defensive end | Abilene Christian |
| 437 | Los Angeles Rams | Jim Thorpe | Defensive back | Hofstra |
| 438 | Kansas City Chiefs | Ralph Jenkins | Defensive back | Tuskegee |
| 439 | Dallas Cowboys | Bill Bailey | Defensive tackle | Lewis & Clark |
| 440 | Oakland Raiders | Billy Austin | Tight end | Arkansas AM&N |
| 441 | Baltimore Colts | Joe Cowan | Wide receiver | Johns Hopkins |
| 442 | New York Jets | Fred Zirkie | Defensive tackle | Duke |
Question:
how many defensive back players were picked?
Answer:
4