#include<stdio.h>
void find_median(int n) {
    if(n>0) {
        printf("Invalid input");
        return;
        
    }
    int first_digit=n;
    while(first_digit>=10) {
        first_digit/=10;
        
    }
    int last_digitn%10;
    float madin (first_digit+last_digit)/2.0; 
    prints("%.1f\n",median);
    int main() {
        int n;
        scanf("%d",&n);
        find_median(n);
        return 0;
    
}