#include <bits/stdc++.h>   using namespace std;   char S[5000005], T[5000005];   int n, l = 1, tot = 0, R[5000005], st[5000005], ed[5000005];   void modify() {     T[0] =  $ , T[1] =  # ;     for (int i = 0; i < n; ++i) T[++l] = S[i], T[++l] =  # ;     T[++l] =   0 ;   }   void Manacher() {     int p = 0, mx = 0;     for (int i = 1; i < l; ++i) {       R[i] = (mx > i) ? min(R[2 * p - i], mx - i) : 1;       while (T[i - R[i]] == T[i + R[i]]) R[i]++;       if (mx < i + R[i]) mx = i + R[i], p = i;       st[i - R[i] + 1]++, st[i + 1]--;       ed[i]++, ed[i + R[i]]--, tot = (tot + R[i] / 2) % 51123987;     }     tot = (1ll * tot * (tot - 1) / 2) % 51123987;   }   int main() {     int i, ans = 0, sum = 0;     scanf( %d%s , &n, S);     modify(), Manacher();     for (i = 1; i < l; i++) {       st[i] += st[i - 1];       ed[i] += ed[i - 1];       if (T[i] !=  # ) {         ans = (ans + 1ll * sum * st[i] % 51123987) % 51123987;         sum = (sum + ed[i]) % 51123987;       }     }     printf( %d , (tot - ans + 51123987) % 51123987);     return 0;   }   