#include<stdio.h>
#include<string.h>
#include<ctype.h>
void findlastwordlenth(const char*s){
    int length=strlen(s);
    if(length<1|| length>20){
        printf("invalid input\n");
        return;
    }
    for(int i=0;i<length;i++){
        if(!isalpha(s[i]) && s[i] !=' '){
            printf("invalid input\n");
            return;
        }
    }
    int i=length-1;
    while(i >=0 && s[i]==' '){
        i--;
    }
    if(i<0){
        return;
    }
    int count=0;
    while(i >=0 && s[i] !=' '){
        count++;
        i--;
    }
    printf("%d\n",count);
}
int main(){
    printf("sample input 1:\n");
    char s1[]="today is monday";
    findLastWordLength(s1);
    printf("sample input 2:\n");
    char s2[]="Hello world";
    findlastwordlength(s2);
    printf("sample input with invalid character:\n");
    char s3[]="Hello world!";
    findlastwordlength(s3);
    return 0;
}
}