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


int main()
{   int a,b;
    scanf("%d%d", &a, &b);
    float n;
    float sar = 0;
    for(a; a <= b ;a++){
            sar += a;
            n++;
    }
    printf("%f", sar/n );
    return 0;
}