O(1)算法

#include <bits/stdc++.h>

#define endl "\n"
#define debug freopen("in.txt","r",stdin),freopen("out.txt","w",stdout)
using namespace std;

int main()
{
    int m,n;
    cin >> m >> n;
    cout << fixed << setprecision(7) << pow(2,n)/pow(2,m) ; 
    return 0;
}