#include <iostream>
#include <string>
#include <cstdlib>.
#include <iomanip>
#include <regex>
#include <math.h>
#include <ctime>
#include <random>
using namespace std;

double fRand(double fMin, double fMax)
{
	double f = (double)rand() / RAND_MAX;
	return fMin + f * (fMax - fMin);
}

int main() {
	double x0, x1, ans, y1, bestx, besty, newp, t = 10000, p, eps = 0.0000000001;
	cout.flush();
	cout.precision(7);
	cout.setf(ios::fixed);
	bestx = fRand(-100, 100);
	cout << "? " << bestx << endl;
	cin >> besty;
	while (t > eps) {
		x1 = bestx + fRand(-25, 25);
		cout << "? " << x1 << endl;
		cin >> y1;
		if (y1 < besty) {
			besty = y1;
			bestx = x1;
		}
		else {
			p = exp(-(y1 - besty) / t);
			newp = fRand(0, 1);
			if (newp <= p) {
				besty = y1;
				bestx = x1;
			}
		}
		t *= 0.99;
	}
	cout << "! " << bestx << endl;
	return 0;
}