What is the difference between Total FY17 PRUs Earned and Vested between Gregory S. Clark and  Nicholas R. Noviello?
{"Gregory S. Clark": {"Total FY17 PRUs Vested at end of FY18": 2404175, "Total FY17 PRUs Vested at end of FY19": 175023, "Total FY17 PRUs Earned and Vested (1)": 2579198}, "Nicholas R. Noviello": {"Total FY17 PRUs Vested at end of FY18": 606935, "Total FY17 PRUs Vested at end of FY19": 44184, "Total FY17 PRUs Earned and Vested (1)": 651119}, "Amy L. Cappellanti-Wolf": {"Total FY17 PRUs Vested at end of FY18": 207142, "Total FY17 PRUs Vested at end of FY19": 15080, "Total FY17 PRUs Earned and Vested (1)": 222222}, "Samir Kapuria": {"Total FY17 PRUs Vested at end of FY18": 148322, "Total FY17 PRUs Vested at end of FY19": 10798, "Total FY17 PRUs Earned and Vested (1)": 159120}, "Scott C. Taylor": {"Total FY17 PRUs Vested at end of FY18": 414287, "Total FY17 PRUs Vested at end of FY19": 30160, "Total FY17 PRUs Earned and Vested (1)": 444447}}
total_prus_earned_vested_gregory = df["Gregory S. Clark"]["Total FY17 PRUs Earned and Vested (1)"]
total_prus_earned_vested_noviello = df["Nicholas R. Noviello"]["Total FY17 PRUs Earned and Vested (1)"]
answer = total_prus_earned_vested_gregory - total_prus_earned_vested_noviello