In 2021, Smith, a divorced person, provided over one-half the support for his widowed mother, Ruth, and his son, Clay, both of whom are U.S. citizens. During 2021, Ruth did not live with Smith. She received $9,850 in Social Security benefits. Clay, a full-time graduate student, and his wife lived with Smith. Clay had no income but filed a joint return for 2021, owing an additional $500 in taxes on his wife's income. How many dependents was Smith entitled to claim on his 2021 tax return?