answer.code: In function ‘int main()’:
answer.code:54:24: error: ‘strlen’ was not declared in this scope
   54 |   scanf("%s",s+0),lena=strlen(s+0);
      |                        ^~~~~~
answer.code:4:1: note: ‘strlen’ is defined in header ‘<cstring>’; did you forget to ‘#include <cstring>’?
    3 | #include<cmath>
  +++ |+#include <cstring>
    4 | #define N 5100010
answer.code:52:10: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
   52 |   freopen("multiple.in","r",stdin);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
answer.code:53:10: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
   53 |   freopen("multiple.out","w",stdout);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~