zoj 2549 So You Want to Be a ...

#include <cstdio>double calc(int n, double t, double x){    if(n == 0)        return x;    double e = calc(n - 1, t, x * 2);    double p = x / e;    if(p <= t)        return (1 + t) / 2.0 * e;    else        return ((p - t) * x + (1 - p) * (1 + p) / 2.0 * e) / (1 - t);}int main(void){    int n;    double t;    while(scanf("%d%lf", &n, &t) != EOF && n > 0) {        printf("%.3lfn", calc(n, t, 1));    }    return 0;}