Language: C

//set many funcs template
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#define inf 1072114514
#define llinf 4154118101919364364
#define mod 1000000007

int max(int a,int b){if(a>b){return a;}return b;}
int min(int a,int b){if(a<b){return a;}return b;}
int zt(int a,int b){return max(a,b)-min(a,b);}
int round(int a,int b){if((a%b)*2 >= b){return (a/b)+1;}return a/b;}
int ceil(int a,int b){if(a%b==0){return a/b;}return (a/b)+1;}
int gcd(int a,int b){int c;while(b!=0){c=a%b;a=b;b=c;}return a;}
int lcm(int a,int b){int c=gcd(a,b);a/=c;return a*b;}
int nCr(int a,int b){int i,r=1;for(i=1;i<=b;i++){r*=(a+1-i);r/=i;}return r;}
int fact(int a){int i,r=1;for(i=1;i<=a;i++){r*=i;}return r;}
int pow(int a,int b){int i,r=1;for(i=1;i<=b;i++){r*=a;}return r;}
long long llmax(long long a,long long b){if(a>b){return a;}return b;}
long long llmin(long long a,long long b){if(a<b){return a;}return b;}
long long llzt(long long a,long long b){return llmax(a,b)-llmin(a,b);}
long long llround(long long a,long long b){if((a%b)*2 >= b){return (a/b)+1;}return a/b;}
long long llceil(long long a,long long b){if(a%b==0){return a/b;}return (a/b)+1;}
long long llgcd(long long a,long long b){long long c;while(b!=0){c=a%b;a=b;b=c;}return a;}
long long lllcm(long long a,long long b){long long c=llgcd(a,b);a/=c;return a*b;}
long long llnCr(long long a,long long b){long long i,r=1;for(i=1;i<=b;i++){r*=(a+1-i);r/=i;}return r;}
long long llfact(long long a){long long i,r=1;for(i=1;i<=a;i++){r*=i;}return r;}
long long llpow(long long a,long long b){long long i,r=1;for(i=1;i<=b;i++){r*=a;}return r;}
double dbmax(double a,double b){if(a>b){return a;}return b;}
double dbmin(double a,double b){if(a<b){return a;}return b;}
double dbzt(double a,double b){return dbmax(a,b)-dbmin(a,b);}
int sortfncsj(const void *a,const void *b){if(*(int *)a>*(int *)b){return 1;}if(*(int *)a==*(int *)b){return 0;}return -1;}
int sortfnckj(const void *a,const void *b){if(*(int *)a<*(int *)b){return 1;}if(*(int *)a==*(int *)b){return 0;}return -1;}
int llsortfncsj(const void *a,const void *b){if(*(long long *)a>*(long long *)b){return 1;}if(*(long long *)a==*(long long *)b){return 0;}return -1;}
int llsortfnckj(const void *a,const void *b){if(*(long long *)a<*(long long *)b){return 1;}if(*(long long *)a==*(long long *)b){return 0;}return -1;}
int dbsortfncsj(const void *a,const void *b){if(*(double *)a>*(double *)b){return 1;}if(*(double *)a==*(double *)b){return 0;}return -1;}
int dbsortfnckj(const void *a,const void *b){if(*(double *)a<*(double *)b){return 1;}if(*(double *)a==*(double *)b){return 0;}return -1;}

int main(void){
    int i,l,t,b,r=0;
    char s[131072]
    scanf("%s",s);
    l = strlen(s);
    t = 0;b = l-1;
    while(t<b){
        if(s[t]=='x'){
            if(s[b] == 'x'){t++;b--;}
            else{r++;t++;}
        }
        else if(s[b]=='x'){
            r++;b--;
        }
        else{
            if(s[t]==s[b]){t++;b--;}
            else{printf("-1\n");return 0;}
        }
    }
    printf("%d\n",r);
    return 0;
}

Compiler output:
main.c:12:5: warning: conflicting types for built-in function 'round'; expected 'double(double)' [-Wbuiltin-declaration-mismatch]
   12 | int round(int a,int b){if((a%b)*2 >= b){return (a/b)+1;}return a/b;}
      |     ^~~~~
main.c:5:1: note: 'round' is declared in header '<math.h>'
    4 | #include<stdlib.h>
  +++ |+#include <math.h>
    5 | #define inf 1072114514
main.c:13:5: warning: conflicting types for built-in function 'ceil'; expected 'double(double)' [-Wbuiltin-declaration-mismatch]
   13 | int ceil(int a,int b){if(a%b==0){return a/b;}return (a/b)+1;}
      |     ^~~~
main.c:13:5: note: 'ceil' is declared in header '<math.h>'
main.c:18:5: warning: conflicting types for built-in function 'pow'; expected 'double(double,  double)' [-Wbuiltin-declaration-mismatch]
   18 | int pow(int a,int b){int i,r=1;for(i=1;i<=b;i++){r*=a;}return r;}
      |     ^~~
main.c:18:5: note: 'pow' is declared in header '<math.h>'
main.c:22:11: warning: conflicting types for built-in function 'llround'; expected 'long long int(double)' [-Wbuiltin-declaration-mismatch]
   22 | long long llround(long long a,long long b){if((a%b)*2 >= b){return (a/b)+1;}return a/b;}
      |           ^~~~~~~
main.c:22:11: note: 'llround' is declared in header '<math.h>'
main.c: In function 'main':
main.c:42:5: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'scanf'
   42 |     scanf("%s",s);
      |     ^~~~~
main.c:42:16: error: 's' undeclared (first use in this function)
   42 |     scanf("%s",s);
      |                ^
main.c:42:16: note: each undeclared identifier is reported only once for each function it appears in