#include<stdio.h>
#include<string.h>
#include<ctype.h>
 int main() {
     char s[21];
     
     printf("Enter a string (up to 20 characters):");
     fgets(s,sizeof(s),stdin);
     s[strcspn(s, "\n")] = 0;
     for(int i=0;s[i] !='\0';i++) {
         if(isascii(s[i]) || isprint(s[i]&&isspace(s[i])) {
             printf("Invalid input.\n");
             return 1;
         }
     }
     int len = strlen(s);
     while (len > 0 && isspace(s[len - 1]))
     {
         s[len - 1] = '\0';
         len--;
     }
     if(len == 0) {
         printf("Invalid input.\n");
         return 1;
     }
     int last_word_length = 0;
     int i = len - 1;
     while (i>=0 && isspace(s[i])) {
         last_word_length++;
         i--;
     }
     printf("%d\n",last_word_length);
     
      return 0;
 }