/in/foo.c:3:1: error: unknown type name 'using'
 using namespace std;
 ^~~~~
/in/foo.c:3:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
 using namespace std;
                 ^~~
/in/foo.c: In function 'readstr':
/in/foo.c:7:6: warning: statement with no effect [-Wunused-value]
     s[100];
     ~^~~~~
/in/foo.c: In function 'main':
/in/foo.c:16:11: warning: implicit declaration of function 'min' [-Wimplicit-function-declaration]
 if(k==1)l[min(x,y)]++,r[max(x,y)]++;
           ^~~
/in/foo.c:16:25: warning: implicit declaration of function 'max' [-Wimplicit-function-declaration]
 if(k==1)l[min(x,y)]++,r[max(x,y)]++;
                         ^~~