#include<stdio.h>
#include<string.h>
#include<ctype.h>

int main(){
    char s[21];
   // printf("Enter a string (max 20 characters): ");
    fgets(s, sizeof(s),stdin);
    s[strcspn(s,"\n")] = 0;
    for(int i=0; s[i] !='\0'; i++){
        if(!isalnum(s[i]) && s[i] != ' '){
        printf("Invalid input\n");
        return 1;
        }
    }
    int length =0;
    int i= strlen(s)-1;
    while(i >=0 && s[i]==''){
        length++;
        i--;
    }
    printf("%d\n", length);
    return 0;
}