题目
题意
定义奇妙数x 为，存在两个正整数b>a,x = b * b - a * a
求第n个奇妙数，1 all odd numbers are avaiable.(expect for 1)
case 2: b and a have the same parity.
---> all numbers, which modulos 4 is 0, is available(expect for 4)
x = 2 * k + 1, k >= 1
x = 4 * k, k >= 1
3, 5, 7, 8, 9, 11, 12
2 * 2 - 1 * 1 = 3,
3 * 3 - 2 * 2 = 5,
4 * 4 - 3 * 3 = 7,
3 * 3 - 1 * 1 = 8
*/
ll n, m, res;
int mp[] = {0, 1, 3};
void solve() {
scanf("%lld", &n);
if (n == 1LL) {
res = 3;
} else {
n -= 1;
res = 4LL + 4 * (n / 3);
n %= 3;
res += mp[n];
}
printf("%lld\n", res);
}
int main() {
int t;
// scanf("%d", &t);
t = 1;
while (t--) {
solve();
}
}
