The input and output drops are due to the input and output queues being overrun by a burst of traffic. This is not related to a buffer problem."No buffer" represents the number of packets dropped because there is no free buffer to copy the packet. If you see "no buffer" drops, buffer tuning may be needed.
Below is a partial output of show buffers:
Middle buffers, 600 bytes (total 150, permanent 25): 147 in free list (10 min, 150 max allowed) 61351931 hits, 137912 misses, 51605 trims, 51730 created 91652 failures (0 no memory)
The number of "failures" and "no memory" are the only areas you need to worry about. Failures may occur, but these should stabilize after a while. The router creates or trims buffers as necessary to stabilize the number of failures. If the number of failures continues to increase, then buffer tuning might be necessary.