用gurobi写以下代码，目标函数是求最小化k，约束条件是100x+y<=135000,y>=3a+[645.32-a+b],645.32-a+b<=k

import gurobipy as gp
from gurobipy import GRB

# Create a new model
m = gp.Model("minimize_k")

# Create variables
x = m.addVar(vtype=GRB.INTEGER, name="x")
y = m.addVar(vtype=GRB.INTEGER, name="y")
a = m.addVar(vtype=GRB.INTEGER, name="a")
b = m.addVar(vtype=GRB.INTEGER, name="b")
k = m.addVar(vtype=GRB.INTEGER, name="k")

# Set objective
m.setObjective(k, GRB.MINIMIZE)

# Add constraints
m.addConstr(100*x + y <= 135000, "c1")
m.addConstr(y >= 3*a + 645.32 - a + b, "c2")
m.addConstr(645.32 - a + b <= k, "c3")

# Optimize model
m.optimize()

# Print solution
print(f"Optimal value of k: {k.X}")