/in/foo.c: In function 'main':
/in/foo.c:11:8: warning: implicit declaration of function 'max'; did you mean 'main'? [-Wimplicit-function-declaration]
  time1=max(n1*t1,n2*t2);
        ^~~
        main
/tmp/ccTgCYr5.o: In function `main':
foo.c:(.text.startup+0x46): undefined reference to `max'
foo.c:(.text.startup+0x75): undefined reference to `max'
collect2: error: ld returned 1 exit status