public class Solution{

```
public int Fn(int n){
int result[] = {0,1,n};
if (n < 2) return n;
for (int i = 2 ;i <= n ; i ++) {
result[2] = result[0] + result[1];
result[0] = result[1];
result[1] = result[2];
}
return result[2];
}
}
```

}