#include<stdio.h>

int main(){
    int n;
    scanf("%d",&n);
    
    if(n<0){
        printf("Invalied input\n");
    }else {
        int first_digit=n;
        while(first_digit>=10){
            first_digit/=10;
        }
        int last_digit=n%10;
        double median=("%d",first_digit+last_digit)/2.0;
        printf("%.1f\n");
       
    }
    return 0;
}