#include <stdio.h>
#include <math.h>

int main() {
    int n, first_digit, last_digit;
    float median;
    
    printf("Enter an integer: ");
    scanf("%d", &n);
    
    if (n < 0) {
        printf("Invalid input\n");
        return 0;
    }
    
    last_digit = n % 10;
    
    first_digit + n;
    while (first_digit >= 10) {
        first_digit /=10;
    }
    
    median = (float)(first_digit + last_digit) / 2.0;
    
    print("%.1f\n", median);
    
    return 0;
}