#include<bits/stdc++.h> #define int long long using namespace std; signed main(){ double x,n; cin>>x>>n; double ans = 0; for (int i = 1;i <= n;i++){ ans += 1.0 * pow(-1.0,(i - 1) & 1) * pow(x,i); } printf("%.2lf",ans); return 0; }