Amtel has announced that it will release a 128-bit computer chip by 2010, a 256-bit computer by 2020, and so on, continuing its strategy of doubling the word-size every ten years. (Amtel released a 64-bit computer in 2000, a 32-bit computer in 1990, a 16-bit computer in 1980, an 8-bit computer in 1970, and a 4-bit computer, its first, in 1960.)
Amtel will use a new benchmark - the Factstone - to advertise the vastly improved capacity of its new chips. The Factstone rating is defined to be the largest integer n such that n! can be represented as an unsigned integer in a computer word.

Given a year 1960 ≤ y ≤ 2160, what will be the Factstone rating of Amtel's most recently released chip?

There are several test cases. For each test case, there is one line of input containing y. A line containing 0 follows the last test case. For each test case, output a line giving the Factstone rating.

Input
1960
1981
0
Output
3
8

思路：n!<2^bit,两边同时取2为底的对数，有log(1*2*3*...*n)<bit;

#include<iostream>
using namespace std;
#include<cstdio>
#include<cmath>
#include<algorithm>
int main(){
	int y,i;
	__int64 t;
	double ans;
	while(scanf("%d",&y)!=-1&&y){
		t=(y-1960)/10+2;
		t=1<<t;
		ans=0;
		i=0;
		while(ans<t)
			ans+=log(double(++i))/log(2.0);
		printf("%d\n",i-1);
	}
}