#include <stdio.h>
#include <string.h>
#include <ctype.h>
int ispalindrome(int n) {
    int reversed = 0, original = n;
    while (n > 0) {
        reversed = reversed * 10 + (n % 10);
        n /= 10;
    }
    return original == reversed;
}
int isvalidnumber(char str[]) {
    int i = 0;
    if (str[0] == '-') return 0;
    while (str[i]) {
        if (!isdigit(str[i]))
        return 0;
        i++;
    }
    return 1;
}
int main() {
    char inputstr[100];
    int num;
    scanf("%s", inputstr);
    if (!isValidNumber(inputstr)) {
        printf("Invalid input\n");
        return o;
    
}