题解 | [NOIP2015]金币
#include <stdio.h>
int main() {
int k,days=0,sum=0,i=1;
scanf("%d",&k);
while(1){
days += i;
if(days>k){
days -= i;
break;
}
sum += i*i;
i++;
}
int left = k-days;
printf("%d\n",sum+i*left);
return 0;
}