poj 3911--Internet Service Providers【求导】

探讨一组互联网服务提供商如何通过私有通信渠道最大化总利润的方法。该渠道拥有固定的容量限制，每个ISP公司需确定最佳的数据传输速率，以实现整体利润的最大化。

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Internet Service Providers

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 600		Accepted: 286

Description

A group of N Internet Service Provider companies (ISPs) use a private communication channel that has a maximum capacity of C traffic units per second. Each company transfers T traffic units per second through the channel and gets a profit that is directly proportional to the factor T(C - TN). The problem is to compute T_optim, the smallest value of T that maximizes the total profit the N ISPs can get from using the channel. Notice that N, C, T, and T_optim are integer numbers.

Input

Each data set corresponds to an instance of the problem above and contains two integral numbers – N and C – with values in the range from 0 to 10 ⁹. The input data are separated by white spaces, are correct, and terminate with an end of file.

Output

For each data set the program computes the value of T_optim according to the problem instance that corresponds to the data set. The result is printed on the standard output from the beginning of a line. There must be no empty lines on the output.

Sample Input

1 0 
0 1 
4 3 
2 8 
3 27 
25 1000000000

Sample Output

Source

Southeastern European Regional Programming Contest 2008

#include<cstdio>
#include<cstring>
int main(){
	long long n, c;
	while(scanf("%lld%lld", &n, &c)!=EOF){
		if(n==0)
			printf("0\n");
		else
		{
			long long a, b, f;
			f = c/2/n;
			a = f*(c - f*n);
			b = (f+1)*(c-(f+1)*n);
			if(a >= b)
				printf("%lld\n",f);
			else
				printf("%lld\n", f+1);	
		}
	}
	return 0;
}