Mobile Network

Time Limit : 8 sec, Memory Limit : 65536 KB

Problem I: Mobile Network

The trafic on the Internet is increasing these days due to smartphones. The wireless carriers have to enhance their network infrastructure.

The network of a wireless carrier consists of a number of base stations and lines. Each line connects two base stations bi-directionally. The bandwidth of a line increases every year and is given by a polynomial f(x) of the year x.

Your task is, given the network structure, to write a program to calculate the maximal bandwidth between the 1-st and N-th base stations as a polynomial of x.

Input

The input consists of multiple datasets. Each dataset has the following format:

N M
u1 v1 p1
...
uM vM pM

The first line of each dataset contains two integers N (2 ≤ N ≤ 50) and M (0 ≤ M ≤ 500), which indicates the number of base stations and lines respectively. The following M lines describe the network structure. The i-th of them corresponds to the i-th network line and contains two integers ui and vi and a polynomial pi. ui and vi indicate the indices of base stations (1 ≤ ui, viN); pi indicates the network bandwidth.

Each polynomial has the form of:

aLxL + aL-1xL-1 + ... + a2x2 + a1x + a0

where L (0 ≤ L ≤ 50) is the degree and ai's (0 ≤ iL, 0 ≤ ai ≤ 100) are the coefficients. In the input,

  • each term aixi (for i ≥ 2) is represented as <ai>x^<i>
  • the linear term (a1x) is represented as <a1>x;
  • the constant (a0) is represented just by digits;
  • these terms are given in the strictly decreasing order of the degrees and connected by a plus sign ("+");
  • just like the standard notations, the <ai> is omitted if ai = 1 for non-constant terms;
  • similarly, the entire term is omitted if ai = 0 for any terms; and
  • the polynomial representations contain no space or characters other than digits, "x", "^", and "+".

For example, 2x2 + 3x + 5 is represented as 2x^2+3x+5; 2x3 + x is represented as 2x^3+x, not 2x^3+0x^2+1x+0 or the like. No polynomial is a constant zero, i.e. the one with all the coefficients being zero.

The end of input is indicated by a line with two zeros. This line is not part of any dataset.

Output

For each dataset, print the maximal bandwidth as a polynomial of x. The polynomial should be represented in the same way as the input format except that a constant zero is possible and should be represented by "0" (without quotes).

Sample Input

3 3
1 2 x+2
2 3 2x+1
3 1 x+1
2 0
3 2
1 2 x
2 3 2
4 3
1 2 x^3+2x^2+3x+4
2 3 x^2+2x+3
3 4 x+2
0 0

Output for the Sample Input

2x+3
0
2
x+2

Source: ACM International Collegiate Programming Contest , ACM-ICPC Japan Alumni Group Practice Contest 2011, Tokyo, 2011-11-06
http://acm-icpc.aitea.net/