#include <stdio.h> 

int main () {
	
	int dd, mm, yy;
	
	printf("Please enter the date dd/mm/yy:\n");
	scanf("%d/%d/%d", &dd, &mm, &yy);

	int bissextile = yy % 400 == 0 || (yy % 4 == 0 && yy % 100 != 0);
	
	
	if (dd>31 || dd<1 || mm>12 || mm<1)
		printf("Invalid date.\n");
  
        if((mm==2 && dd<30 && bissextile) || (mm==2 && dd<29 && bissextile==0))
            printf("valid date.\n");
        else
			if((mm==4 || mm==6 || mm==9 || mm==11)&& dd<31)
				printf("valid date.\n");
			else
				if(dd<31 && mm!=2)
					printf("valid date.\n");
                 else
                    printf("Invalid date.\n");
		
	return 0;
}