YES(?, a + 3)

Initial complexity problem:
1:	T:
		(?, 1)    f300(a, b, c) -> f300(a - 1, a - 2, c) [ a >= 1 /\ b + a >= 1 /\ b >= 1 ]
		(?, 1)    f300(a, b, c) -> f1(a, b, d) [ a >= 1 /\ 0 >= b + a /\ b >= 1 ]
		(?, 1)    f300(a, b, c) -> f1(a, b, d) [ b >= 1 /\ 0 >= a ]
		(?, 1)    f300(a, b, c) -> f1(a, b, d) [ 0 >= b ]
		(1, 1)    f2(a, b, c) -> f300(a, b, c)
	start location:	f2
	leaf cost:	0

Testing for unsatisfiable constraints removes the following transition from problem 1:
	f300(a, b, c) -> f1(a, b, d) [ a >= 1 /\ 0 >= b + a /\ b >= 1 ]
We thus obtain the following problem:
2:	T:
		(?, 1)    f300(a, b, c) -> f300(a - 1, a - 2, c) [ a >= 1 /\ b + a >= 1 /\ b >= 1 ]
		(?, 1)    f300(a, b, c) -> f1(a, b, d) [ b >= 1 /\ 0 >= a ]
		(?, 1)    f300(a, b, c) -> f1(a, b, d) [ 0 >= b ]
		(1, 1)    f2(a, b, c) -> f300(a, b, c)
	start location:	f2
	leaf cost:	0

Repeatedly removing leaves of the complexity graph in problem 2 produces the following problem:
3:	T:
		(?, 1)    f300(a, b, c) -> f300(a - 1, a - 2, c) [ a >= 1 /\ b + a >= 1 /\ b >= 1 ]
		(1, 1)    f2(a, b, c) -> f300(a, b, c)
	start location:	f2
	leaf cost:	2

A polynomial rank function with
	Pol(f300) = V_1
	Pol(f2) = V_1
orients all transitions weakly and the transition
	f300(a, b, c) -> f300(a - 1, a - 2, c) [ a >= 1 /\ b + a >= 1 /\ b >= 1 ]
strictly and produces the following problem:
4:	T:
		(a, 1)    f300(a, b, c) -> f300(a - 1, a - 2, c) [ a >= 1 /\ b + a >= 1 /\ b >= 1 ]
		(1, 1)    f2(a, b, c) -> f300(a, b, c)
	start location:	f2
	leaf cost:	2

Complexity upper bound a + 3

Time: 0.143 sec (SMT: 0.136 sec)