/in/foo.c: In function 'main':
/in/foo.c:10:20: warning: implicit declaration of function 'sqrt' [-Wimplicit-function-declaration]
   for (n=2;n<=(int)sqrt((double)m);n++){
                    ^~~~
/in/foo.c:10:20: warning: incompatible implicit declaration of built-in function 'sqrt'
/in/foo.c:10:20: note: include '<math.h>' or provide a declaration of 'sqrt'