#include <stdio.h> #define STUDENT_NUM 30 int main(void) { int student[STUDENT_NUM+1] = {0, }; int num; for (int i = 0; i < 28; i++) { scanf("%d", &num); student[num] = num; } for (int i = 1; i <= STUDENT_NUM; i++) { if (student[i] == 0) printf("%d\n", i); } }