#include <iostream>
#include <cmath>
int main()
{
    unsigned long long a;
    while(std::cin>>a)
    {
        if(a==1)
        {
            std::cout<<"0\n";
            continue;
        }
        std::cout<<(-1+sqrt(8*a-7))/2<<"\n";
    }
    return 0;
}