n, k= list(map(int,str.split(input())))
max_pos=(((k-1)*k)//2)+1
if n==1:
print(0)
elif n<=k:
print(1)
elif n>max_pos:
print(-1)
else:
m=((1+(1-(4*(n-max_pos)*2))**0.5)/2)
if m*(m-1)+n>max_pos:
m-=1
print(int(k-m))// Online C++ compiler to run C++ program online
#include <bits/stdc++.h>
using namespace std;
int main() {
long long n,k;
cin>>n>>k;
long long low=0,high=k;
long long maxpipes=(k*(k-1))/2+1;
while(low<=high){
long long mid=low+(high-low)/2;
long long poss=(k*mid)-((mid*(mid+1))/2)+1;
if(poss<n)low=mid+1;
else high=mid-1;
}
if(low>k){
cout<<-1;
}else cout<<low;
return 0;
}1547B - Alphabetical Strings | 1550A - Find The Array |
118B - Present from Lena | 27A - Next Test |
785. Is Graph Bipartite | 90. Subsets II |
1560A - Dislike of Threes | 36. Valid Sudoku |
557. Reverse Words in a String III | 566. Reshape the Matrix |
167. Two Sum II - Input array is sorted | 387. First Unique Character in a String |
383. Ransom Note | 242. Valid Anagram |
141. Linked List Cycle | 21. Merge Two Sorted Lists |
203. Remove Linked List Elements | 733. Flood Fill |
206. Reverse Linked List | 83. Remove Duplicates from Sorted List |
116. Populating Next Right Pointers in Each Node | 145. Binary Tree Postorder Traversal |
94. Binary Tree Inorder Traversal | 101. Symmetric Tree |
77. Combinations | 46. Permutations |
226. Invert Binary Tree | 112. Path Sum |
1556A - A Variety of Operations | 136. Single Number |