A

#include <bits/stdc++.h>

using namespace std;

using LL = long long;

LL n;

signed main() {
  // freopen("in", "r", stdin);
  while (cin >> n) {
    LL tmp = (LL)sqrt(n);
    LL x = tmp * tmp, y = (tmp + 1) * (tmp + 1);
    if (abs(x - n) > abs(y - n)) cout << y << endl;
    else cout << x << endl;
  }
  return 0;
}

B

#include <bits/stdc++.h>

using namespace std;

using LL = long long;

inline bool scan_d(int &num) {
  char in;bool IsN=false;
  in=getchar();
  if(in==EOF) return false;
  while(in!='-'&&(in<'0'||in>'9')) in=getchar();
  if(in=='-'){ IsN=true;num=0;}
  else num=in-'0';
  while(in=getchar(),in>='0'&&in<='9'){
    num*=10,num+=in-'0';
  }
  if(IsN) num=-num;
  return true;
}

const int maxn = 1000100;
int n, q;
int a[maxn];
int vis[1 << 22];

signed main() {
  // freopen("in", "r", stdin);
  memset(vis, 0, sizeof vis);
  scan_d(n); scan_d(q);
  for (int i = 1; i <= n; i++) {
    scan_d(a[i]);
    vis[a[i]]++;
  }
  while (q--) {
    int k, x, y;
    scan_d(k); scan_d(x); scan_d(y);
    if ((a[x] ^ a[y]) == k) {
      printf("%d\n", 1);
      continue;
    }
    if (vis[a[x] ^ k] && vis[a[y] ^ k]) {
      if ((a[x] ^ k) == (a[y] ^ k)) printf("%d\n", 2);
      else printf("%d\n", -1);
      continue;
    }
    printf("-1\n");
  }
  return 0;
}

C

#include <bits/stdc++.h>

using namespace std;

using LL = long long;

inline bool scan_d(LL &num) {
  char in;bool IsN=false;
  in=getchar();
  if(in==EOF) return false;
  while(in!='-'&&(in<'0'||in>'9')) in=getchar();
  if(in=='-'){ IsN=true;num=0;}
  else num=in-'0';
  while(in=getchar(),in>='0'&&in<='9'){
    num*=10,num+=in-'0';
  }
  if(IsN) num=-num;
  return true;
}

const int maxn = 1001000;
LL n;
LL a[maxn], tot[maxn];

signed main() {
  // freopen("in", "r", stdin);
  scan_d(n);
  LL ret = 0;
  for (int i = 1; i <= n; i++) {
    scan_d(a[i]);
    tot[i] = abs(a[i] - a[i - 1]);
  }
  LL x = INT_MAX, y = INT_MAX;
  for (int i = 2; i <= n; i++) {
    if (y == INT_MAX) y = tot[i];
    else y = __gcd(y, tot[i]);
  }
  x = (y - (a[1] % y)) % y;
  printf("%lld %lld\n", y, x);
  return 0;
}