int main(int argc, char *argv[])
{
setIO("sample");
n = gi;
if(n % 2 == 0){
printf("NOT POSSIBLE\n");closeIO();return 0;
}
bool unique = true;
scanf("%s",a+1);
pow[0].v = 1;
for(int i = 0;i<=n;++i)
pow[i+1] = pow[i]*int65(p);
for(int i = 1;i<=n;++i) pre[i] = (pre[i-1]*int65(p)+int65(a[i]));
b[0] = pre[n/2];
b[1] = (pre[n]-((pre[n/2+1])*(pow[n/2])));
int ans = 0;
if(b[0] ==b[1]){printf("%s",&a[n/2+2]); closeIO();return 0;}
for(int i = 1;i<=n/2;++i)
if(getnew(1,i-1)*pow[n/2-i+1]+getnew(i+1,n/2+1)==b[1])
ans = ans? (unique = false):i;
for(int i = n/2+2;i<=n;++i)
if(getnew(n/2+1,i-1)*pow[n-i]+getnew(i+1,n) == b[0])
ans = ans? (unique = false):i;
if(unique){
if(ans == 0)
printf("NOT POSSIBLE");
else if(ans <= n/2+1)
printf("%s",&a[n/2+2]);
else
for(int i = 1;i<=n/2;++i) printf("%c",a[i]);
puts("");
}
else printf("NOT UNIQUE\n");
closeIO();
return EXIT_SUCCESS;
}
/*
inserts an element after a given element (prev_data)
prev_data content of the previous element
data content of the new element
data_size size of data
//*/
int insertelement(const char* prev_data, const unsigned int prev_data_size, const char* data, const unsigned int data_size)
{
// checks
if(NULL == data) return -1;
// special case: if prev_data is null - prepend the new element
if(NULL == prev_data){
element_t* tmp = NULL;
if(NULL == (tmp = getnew())){
return -1;
}
if(0 != init(tmp, data, data_size)){
return -1;
}
// relink - last is already set correctly
tmp->next = first;
first = tmp;
// if tmp is the only element added, set last, too
if(NULL == last){
last = first;
}
return 0;
}
// normal case: prev elements
// TODO get prev
// new element
element_t* tmp = find(data, data_size);
// TODO: what if no tmp was found
// next element
element_t* next = prev->next;
// TODO, the next
// relink elements
tmp->next = next;
prev->next = tmp;
return 0;
}
