WA on #10

90pts:

#include <bits/stdc++.h>
#define int long long
using namespace std;
const int N=1001;
int m,n;
int a[N]={0},b[N]={0},c[N]={0},x=1000;
void f(int a[],int b[]){
    for(int i=1;i<=1000;i++) a[i]+=b[i];
    for(int i=1;i<=1000;i++){
        if(a[i]>=10){
            a[i+1]+=a[i]/10;
            a[i]%=10;
        }
    }
}
void swapx(int a[],int b[]){
    for(int i=1;i<=1000;i++) a[i]=b[i];
}
signed main(){
    cin>>n;
    a[1]=1;
    b[1]=2;
    if(n<=3){
        cout<<n;
        exit(0);
    }
    for(int i=3;i<=n/*-m-2*/;i++){
        f(a,b);
        swapx(c,a);
        swapx(a,b);
        swapx(b,c); 
    }
    for(int i=1000;i>=1;i--){
        if(c[i]==0) x--;
        else break;
    }
    for(int i=x;i>=1;i--) cout<<c[i];
    return 0;
}