上海市计算机学会2020年9月的（丙组）竞赛

 #include <iostream>

    
 #include <algorithm>
    
 #include <cmath>
    
 using namespace std;
    
 int ct, ct1, sum = 0;
    
 int main() {
    
 	int num, ct = 1, mx = -1;
    
 	cin >> num;
    
 	for (int i = num/2; i >= 1; --i) {
    
 		if (num%i == 0) {
    
 			ct1 = i;
    
 			ct = sqrt(i);
    
 			if ( pow(ct, 2) == ct1) {
    
 				sum = ct1;
    
 				mx = max(mx, sum);
    
 			}
    
 		}
    
 	}
    
 	printf("%d", mx);
    
 	return 0;
    
 }