#include <iostream> using namespace std; long long factorial(int n); int main() { int n; cin >> n; cout << factorial(n) << endl; return 0; } long long factorial(int n) { // write your code here...... if(n==1 || n==0) return 1; else if(n>1) return n*factorial(n-1); else return -1; //返回-1即表示该数据不存在阶乘 }