Query logging time, not values

HiI have a database and ~150 clients non-stop writing to this database quite
big pieces of text.
I have a performacne problem so I tried to increase log level, so I could
see which queries take most time.
My postgresql.conf (Log section) is:

log_destination = 'stderr'
logging_collector = on
log_rotation_size = 1GB
log_connections = on
log_line_prefix = '%m %p %u %d %r '
log_lock_waits = on
log_statement = 'ddl'
log_temp_files = 4096

And I got the query times + query parameters values, which makes my log
extremly big.
How can I set the logging parameters to write query + duration time but
without parameter values?

Thanks
Ludwik

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Ludwik Dyląg