#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main(){
    char s[21];
    int length = 0;
    int has_special-char = 0;
    printf("Enter a string(up to 20 characters):");
    scanf("%[^\n",s);
    for (int i = 0;s[i]!='\0';i++){
        if(!isspace(s[i])&&!isalnum(s[i])){
            has_special-char=1;
            break;
        }
    }
    if(has_special_char){
        printf("Invalid input\n");
    }else{
        int len=strlen(s);
        int last_word_start=-1;
        for(int i=len-1;i>=0;i--){
            last_word_start==-1;
            for(int i=len-1;i>=0;i--){
                if(s[i]!=''){
                    if(last_word_start==-1){
                        break;
                    }
                }
                if(last_word_start!=-1){
                    length=last_word_start-(strrchr(s,'')?strrchr(s,'')-s:-1);
                }
                printf("%d\n",length);
            }
            return 0
        }
    }
}