#include<bits/stdc++.h>
using namespace std;
#define int long long
signed main()
{
	int x;cin>>x;
	int l=0,r=62,ans=0;
	while(l<=r)
	{
		int mid=(l+r)>>1;
		if((1ll<<mid)<=x)l=mid+1,ans=mid;
		else r=mid-1; 
	}
	cout<<ans<<'\n';
	return 0;
}