//-------------------------------------------------------------
// Segment tree
//   in some general form
//
// Verified by
//   - Codeforces 104 E
//-------------------------------------------------------------

class SegmentTree
{
	// --- DATA FOR EACH NODE ---
	struct Node
	{
		int sum;
		int maxLeft;
		int minLeft;
		int n4;
		int n7;
		bool switched;
	};
	// --- DATA FOR EACH NODE ---

	Node Canonical(int lv, int idx)
	{
		Node& x = tree[lv][idx];
		// --- DO SOMETHING IF YOU NEED CANONICALIZATION ---
		if( !x.switched )
			return x;
		Node n = {-x.sum, -x.minLeft, -x.maxLeft, x.n7, x.n4, false};
		return n;
		// --- DO SOMETHING IF YOU NEED CANONICALIZATION ---
	}

	void UpdateMidNode(int lv, int idx)
	{
		Node l = Canonical(lv-1, idx*2);
		Node r = Canonical(lv-1, idx*2+1);
		// --- BOTTOM UP COMPUTATION ---
		Node me = {
			l.sum + r.sum,
			max(l.maxLeft, l.sum+r.maxLeft),
			min(l.minLeft, l.sum+r.minLeft),
			l.n4 + r.n4,
			l.n7 + r.n7,
			false
		};
		// --- BOTTOM UP COMPUTATION ---
		tree[lv][idx] = me;
	}

	vector< vector<Node> > tree;

public:
	SegmentTree(const string& s)
	{
		int N = 1;
		while( N < s.size() )
			N <<= 1;

		tree.resize(tree.size()+1); tree.back().resize(N);
		for(int i=0; i<N; ++i)
		{
			// --- INITIALIZE BASE 1-ELEMENT NODES ---
			int v = i<s.size() ? (s[i]=='4' ? +1 : -1) : 0;
			Node me = {v, max(0,v), min(0,v), v==+1, v==-1, false};
			// --- INITIALIZE BASE 1-ELEMENT NODES ---
			tree.back()[i] = me;
		}

		while(N>>=1)
		{
			tree.resize(tree.size()+1); tree.back().resize(N);
			for(int i=0; i<N; ++i)
				UpdateMidNode(tree.size()-1, i);
		}
	}

	int Count()
	{
		Node x = Canonical(tree.size()-1, 0);
		return x.maxLeft + x.n7;
	}

	void Switch(int L, int R)
	{
		SwitchRec(tree[0].size(), tree.size()-1, 0, L, R);
	}

	void SwitchRec(int Stride, int lv, int idx, int Raw_L, int Raw_R)
	{
		// Outside
		if( Raw_R <= Stride*idx || Stride*(idx+1) <= Raw_L )
			return;

		// Inside
		bool& me = tree[lv][idx].switched;
		if( Raw_L <= Stride*idx && Stride*(idx+1) <= Raw_R )
		{
			me ^= 1;
			return;
		}

		// Overlap
		tree[lv-1][idx*2].switched   ^= me;
		tree[lv-1][idx*2+1].switched ^= me;
		SwitchRec(Stride/2, lv-1, idx*2,   Raw_L, Raw_R);
		SwitchRec(Stride/2, lv-1, idx*2+1, Raw_L, Raw_R);
		UpdateMidNode(lv, idx);
	}
};
