http://acm.pku.edu.cn/JudgeOnline/problem?id=1183
Код:
#include <stdio.h>
int main(){
unsigned long a,i;
scanf("%ld",&a);
for(i=a;;i--)if((a*a+1)%i==0)break;
printf("%ld\n",2*a+(a*a+1)/i+i);
}