./glpsol --math -o solution.txt color.txt

GLPSOL: GLPK LP/MIP Solver, v4.55
Parameter(s) specified in the command line:
 --math -o solution.txt color.txt
Reading model section from color.txt...
Reading data section from color.txt...
139 lines were read
Checking (line 23)...
Checking (line 59)...
Display statement at line 66
nc = 4
Generating map...
Generating arc...
Generating obj...
Model has been successfully generated
GLPK Integer Optimizer, v4.55
192 rows, 80 columns, 596 non-zeros
80 integer variables, all of which are binary
Preprocessing...
191 rows, 80 columns, 592 non-zeros
80 integer variables, all of which are binary
Scaling...
 A: min|aij| =  1.000e+00  max|aij| =  1.000e+00  ratio =  1.000e+00
Problem data seem to be well scaled
Constructing initial basis...
Size of triangular part is 191
Solving LP relaxation...
GLPK Simplex Optimizer, v4.55
191 rows, 80 columns, 592 non-zeros
      0: obj =   0.000000000e+00  infeas =  8.600e+01 (0)
*    76: obj =   3.000000000e+00  infeas =  0.000e+00 (0)
*    85: obj =   2.000000000e+00  infeas =  0.000e+00 (0)
OPTIMAL LP SOLUTION FOUND
Integer optimization begins...
+    85: mip =     not found yet >=              -inf        (1; 0)
+   193: >>>>>   4.000000000e+00 >=   2.000000000e+00  50.0% (9; 0)
+   846: mip =   4.000000000e+00 >=     tree is empty   0.0% (0; 47)
INTEGER OPTIMAL SOLUTION FOUND
Time used:   0.1 secs
Memory used: 0.5 Mb (571084 bytes)
1 2
2 1
3 4
4 4
5 1
6 3
7 2
8 4
9 1
10 3
11 3
12 3
13 4
14 2
15 2
16 3
17 4
18 1
19 1
Model has been successfully processed
Writing MIP solution to 'solution.txt'...