include <bits/stdc++.h>

using namespace std;

int main()

{

double d = 10, m, s;
int t;
cin >> m;
if (m <= 10) cout << 1 << endl;
else
{
    while (s < m)
    {
        s += d;
        d += d * 0.1;
        t++;
    }
    if (s < m) cout << t + 1 << endl;
    else cout << t << endl;
}
return 0;

}