UVA 10900 So you want to be a 2n-aire?

#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <stack>
#include <queue>
#include <cctype>
#include <cstdio>
#include <string>
#include <vector>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
#define LL long long
#define PI 3.1415926535897932626
using namespace std;
int gcd(int a, int b) {return a % b == 0 ? b : gcd(b, a % b);}
#define MAXN 35
double v[MAXN],ans,T;
int N;
int main()
{
v[0]=1;
for (int i=1;i<=30;i++) v[i]=v[i-1]*2;
while (scanf("%d%lf",&N,&T)!=EOF)
{
if (N==0 && T==0) break;
if (fabs(1-T)<1e-9) {printf("%.3lf\n",v
);continue;}
double ans=v
;
for (int i=N-1;i>=0;i--)
{
double f=v[i]/ans;
if (f<=T)  ans=(1+T)/2*ans;
else ans=(f-T)/(1-T)*v[i]+(1-f)/(1-T)*(1+f)/2*ans;
}
printf("%.3lf\n",ans);
}
return 0;
}