X
2
4.5.
5
7
10
0
0,15 0,2
0,1
0,1
0,45​

My name is .. and I am a schoolboy . I like going to school and I really like to study. I go to school five days a week. We have classes on Monday, Tuesday, Wednesday, Thursday and Friday. We are free on Saturday and Sunday. My typical school day starts at 7 a.m. My alarm clock rings and I get up and sometimes do my morning exercises. Of course, I clean my teeth and wash my face but I never have breakfast at home. I prefer to take an apple with me and have a snack after the first lesson. I don't have to think about my dress because school uniform is compulsory and we must wear it every day. So it doesn't take me much time to get dressed. Usually I walk to school as I live not very far from it, but sometimes one of my parents drop me off there. Our lessons begin at 8 a.m and we usually have five or six of them every day. As I have already mentioned, I never have breakfast at home, so sometimes I have lunch at school, but I am not a big eater. As for classes, they finish at 2 p.m and then we are free. But I have extra classes of Algebra and Geometry as I am not very good at them. They last till 3 o'clock and after that I go home. When I come home I do my homework and watch TV. Three days a week I go to the swimming pool and twice a week I play tennis. In the evening I chat with my friends online or read books. I go to bed at 11 p.m.That's my typical day.

В картинках два
1-ый посчитать "в лоб" все суммы до n=12. Это довольно быстро.
2-ой длиннее, зато "высокоинтеллектуальный" :) и годится для чисел существенно больших  2018.
1) Вначале выводим общую формулу для суммы (можно не выводить, если помните ее) S[n]=1²+2²+3²+...+n²=n(n+1)(2n+1)/6.
2) Потом из нее выводим формулу для суммы из левой части условия: 1²+3²+5²+...+(2n-1)²=S[2n]-4S[n]=n(4n²-1)/3.
3) Затем легко прикинуть, что если эта сумма около 2018, то n около 11.
4) Проверяем n=11 и 12 и находим n=11.