/in/foo.cc: In function 'int spfa(int)':
/in/foo.cc:40:19: warning: unused variable 'step' [-Wunused-variable]
     int i,j,k,u,v,step,res=0;
                   ^~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:70:13: warning: unused variable 'k' [-Wunused-variable]
     int i,j,k;
             ^