''' ma,klncjvqfh'ofdwpxkla knsdjgvr3p2etqwfklsc,;vm dnbwepvgqfr'mcl EA$VKPJkfo[qe a'vmdrbwjo[5htwrml;DVBRWwwwwwwgm;sdddddd Rbwgpppppppppppppppppppppppppppppppppppppppppppppppppppppsjbfm fj rrrrrrrrrrrrrrrrrrr

#include<bits/stdc++.h>
using namespace std;
int f(int x){
	if(x==1) return 0;
	if(x==2) return 1;
	return f(x-1)+f(x-2);
}
int main()
{
	int n;
	cin>>n;
	cout<<f(n);
	return 0;
}

有好心人发个题解码