Go Home(UPC)

Go Home(UPC)

There is a kangaroo at coordinate 0 on an infinite number line that runs from left to right, at time 0. During the period between time i−1 and time i, the kangaroo can either stay at his position, or perform a jump of length exactly i to the left or to the right. That is, if his coordinate at time i−1 is x, he can be at coordinate x−i, x or x+i at time i. The kangaroo’s nest is at coordinate X, and he wants to travel to coordinate X as fast as possible. Find the earliest possible time to reach coordinate X.

Constraints
X is an integer.
1≤X≤1e9
*

input

6

output

3

*思路：
情况1：当第i点时恰好走到x，为最佳状态，此时直接输出i;
情况2：当第i点时恰好超过x，当第i-1点时恰好小于x；直接输出i就可；
因为假设第i点走了s（s>x）则我可以在第（s-x）点时不动（少走了（s-x）），恰好补回了那点差距，则可以在第i点直接到x位置；

#include<bits/stdc++.h>
using namespace std;
int main(){
	int x,i,t;
	cin>>x;
	for(i=1;;i++) {
		t=(i*(i+1))/2;
		if(t>=x) break;
	}
	cout<<i;
	return 0;
}