#include <iostream>


using namespace std;
using i64 = int64_t;

int main(){
    i64 N; cin >> N;
    auto countShade = [N](i64 showCnt) -> bool {
        i64 height = N - showCnt;
        height -= (N - 1 - height) * 2;
        for(i64 baseHeight = N; baseHeight >= N-showCnt+3; baseHeight--){
            if(height <= 0) return true;
            height -= (baseHeight - 3 - height) * 2 + 3;
        }
        return height <= 0;
    };

    i64 c = 1;
    while(!countShade(c)) c++;
    cout << (N-c) << '\n';

    return 0;
}