High cycle fatigue data for an alloy at various alternating stresses, σ_a (see figure) is given below. A specimen of this alloy is subjected to multiple stress cycles sequentially in the following order: (i) first 5000 cycles at σ_a=400 MPa followed by (ii) 25000 cycles at σ_a=300 MPa and finally (iii) at σ_a=500 MPa. Assuming that Miner's law is obeyed, the number of cycles to failure at the final applied stress of 500 MPa is _______.