#include "bits/stdc++.h"

using namespace std;

void solve()
{
	int l, r, m;
	cin >> l >> r >> m;
	if (l+m<=r)
	{
		cout << m << endl;
		return;
	}
	l %= m;
	r %= m;

	cout << (r-l+1+m)%m << endl;
}

int main()
{
	solve();
	//cout << "yui(*-v・)yui" << endl;
	return 0;
}