C++ :

#include <iostream>
using namespace std;
 
int main(){ 
    int n,s=0,i=0;
    cin>>n;
    
    while(s<n){
    	i++;
    	s+=i;	
	}
	cout<<i<<endl;
}

Python :

n = int(input())
t = []
for i in range(1, n + 1):
    for j in range(1, i + 1):
        t.append(i)
print(t[n - 1])