/in/foo.cc: In function 'int main()':
/in/foo.cc:59:25: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   freopen(buf,"r",stdin);
                         ^
/in/foo.cc:61:26: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   freopen(buf,"w",stdout);
                          ^
/in/foo.cc:66:23: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   int N;scanf("%d",&N);
                       ^
/in/foo.cc:71:32: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     int a,x;scanf("%d%d",&a,&x);
                                ^
/in/foo.cc:76:39: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     int a,b,v;scanf("%d%d%d",&a,&b,&v);
                                       ^
/in/foo.cc:81:25: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     int n;scanf("%d",&n);
                         ^