https://www.acmicpc.net/problem/2748
#include <iostream>
using namespace std;
int n;
// 피보나치 수2
long long solution(){
if(n == 0)
return 0;
long long f = 0;
long long s = 1;
for(int i=2;i<=n;i++){
long long temp = f+s;
f = s;
s = temp;
}
return s;
}
#include<stdio.h>
long long fb[91]={0,1},N,i;int main(){scanf("%lld",&N);while(++i<N)fb[i+1]=fb[i-1]+fb[i];printf("%lld\n",fb[N]);}