count the number of patients who have been diagnosed with malign neopl prostate and did not come back to the hospital within the same month until 2103.
select ( select count( distinct t1.subject_id ) from ( select admissions.subject_id, diagnoses_icd.charttime from diagnoses_icd join admissions on diagnoses_icd.hadm_id = admissions.hadm_id where diagnoses_icd.icd9_code = ( select d_icd_diagnoses.icd9_code from d_icd_diagnoses where d_icd_diagnoses.short_title = 'malign neopl prostate' ) and strftime('%y',diagnoses_icd.charttime) <= '2103' ) as t1 ) - ( select count( distinct t2.subject_id ) from ( select admissions.subject_id, diagnoses_icd.charttime from diagnoses_icd join admissions on diagnoses_icd.hadm_id = admissions.hadm_id where diagnoses_icd.icd9_code = ( select d_icd_diagnoses.icd9_code from d_icd_diagnoses where d_icd_diagnoses.short_title = 'malign neopl prostate' ) and strftime('%y',diagnoses_icd.charttime) <= '2103' ) as t2 join admissions on t2.subject_id = admissions.subject_id where t2.charttime < admissions.admittime and strftime('%y',admissions.admittime) <= '2103' and datetime(t2.charttime,'start of month') = datetime(admissions.admittime,'start of month') )