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

void reverse(char*str,int index){
    if(index<0)return;
    putchar(str[index]);
    reverse(str,index-1);
}

int containdigit(char*str){
    for(int i=0;str[i];i++){
        if(isdigit(str))return 1;
    }
    return 0;
}
int main(){
    char sentence[101];
    fgets(sentence,sizeof(sentence),stdin);
    size_t len=strlen(sentence);
    if(sentence[len-1]=='\n')sentence[len-1]='\0';
    if(containsDigit(sentence)){
        printf("invalid input\n");
    }else{
        reverse(sentence,strlen(sentence)-1);
        printf("\n");
    }
    return 0;
    }