#include<stdio.h> long long Fib(int n) { long long a = 1; long long b = 1; long long sum = 0; if(n<=0) return 0; else if(n==1 || n==2) return 1; else{ while(n>=3) { sum = a + b; a = b; b = sum; n--; if(sum<0) return 0; } } return sum; } int main() { int n; scanf("%d",&n); if(n>2018) return 0; long long ret = Fib(n); if(ret<0) return 0; printf("%u\n",ret); return 0; } 斐波拉契 为啥不过 奇了怪