https://www.acmicpc.net/problem/10870
#include <stdio.h>
#include <iostream>
using namespace std;
int n;
long long solution(){
long long first = 0;
long long second = 1;
if(n == 0)
return first;
for(int i=2;i<=n;i++){
long long temp = first + second;
first = second;
second = temp;
}
return second;
}