what is the total number of different builders in the table?
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col : number | builder | entered service | withdrawn | notes row 1 : 439 | nzr addington | 9-1-1909 | 2-3-1957 | converted to 4-cylinder simple, 6-1949 row 2 : 440 | nzr addington | 25-3-1909 | 2-3-1957 | converted to 4-cylinder simple, 7-1948 row 3 : 441 | nzr addington | 10-5-1909 | 2-3-1957 |  row 4 : 442 | nzr addington | 10-7-1909 | 4-3-1944 | converted to 4-cylinder simple, 6-1943. in use oha row 5 : 443 | nzr addington | 1-12-1909 | 2-3-1957 | converted to 4-cylinder simple, 7-1947 row 6 : 444 | nzr addington | 3-2-1910 | 2-3-1957 | converted to 4-cylinder simple, 12-1949 row 7 : 445 | nzr addington | 24-5-1910 | 26-5-1949 |  row 8 : 446 | nzr addington | 30-4-1910 | 6-12-1946 | converted to 4-cylinder simple, 12-1946. in use oha row 9 : 588 | nzr addington | 14-10-1913 | 2-3-1957 | converted to 4-cylinder simple, 5-1951 row 10 : 589 | nzr addington | 11-11-1949 | 6-1949 |  row 11 : 590 | nzr addington | 27-1-1914 | 2-3-1957 |  row 12 : 591 | nzr addington | 17-3-1914 | 2-3-1957 | converted to 4-cylinder simple, 12-1950 row 13 : 592 | nzr addington | 22-6-1914 | 2-3-1957 | converted to 4-cylinder simple, 10-1950 row 14 : 593 | nzr addington | 3-9-1914 | 2-3-1957 | converted to 4-cylinder simple, 6-1950 row 15 : 594 | nzr addington | 31-10-1914 | 2-3-1957 | converted to 4-cylinder simple, 5-1945 row 16 : 595 | nzr addington | 3-12-1914 | 2-3-1957 |  row 17 : 596 | nzr addington | 26-1-1915 | 2-3-1957 | converted to 4-cylinder simple, 12-1949 row 18 : 597 | nzr addington | 1-4-1915 | 2-3-1957 |
what is the total number of different builders in the table?
Number Builder Entered service Withdrawn Notes
439 NZR Addington 9-1-1909 2-3-1957 Converted to 4-cylinder simple, 6-1949
440 NZR Addington 25-3-1909 2-3-1957 Converted to 4-cylinder simple, 7-1948
441 NZR Addington 10-5-1909 2-3-1957
442 NZR Addington 10-7-1909 4-3-1944 Converted to 4-cylinder simple, 6-1943. In Use Ohai Railway Board 1944-1968. Preserved at Feilding and District Steam Rail Society
443 NZR Addington 1-12-1909 2-3-1957 Converted to 4-cylinder simple, 7-1947
444 NZR Addington 3-2-1910 2-3-1957 Converted to 4-cylinder simple, 12-1949
445 NZR Addington 24-5-1910 26-5-1949
446 NZR Addington 30-4-1910 6-12-1946 Converted to 4-cylinder simple, 12-1946. In Use Ohai Railway Board 1946-1959.
588 NZR Addington 14-10-1913 2-3-1957 Converted to 4-cylinder simple, 5-1951
589 NZR Addington 11-11-1949 6-1949
590 NZR Addington 27-1-1914 2-3-1957
591 NZR Addington 17-3-1914 2-3-1957 Converted to 4-cylinder simple, 12-1950
592 NZR Addington 22-6-1914 2-3-1957 Converted to 4-cylinder simple, 10-1950
593 NZR Addington 3-9-1914 2-3-1957 Converted to 4-cylinder simple, 6-1950
594 NZR Addington 31-10-1914 2-3-1957 Converted to 4-cylinder simple, 5-1945
595 NZR Addington 3-12-1914 2-3-1957
596 NZR Addington 26-1-1915 2-3-1957 Converted to 4-cylinder simple, 12-1949
597 NZR Addington 1-4-1915 2-3-1957
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