#include <bits/stdc++.h>
using namespace std;
int rd() {
bool neg = 0; char c = getchar(); for(; c < '0' || c > '9'; c = getchar()) if(c == '-') neg = !neg;
int n = 0; while('0' <= c && c <= '9') n = (n << 3) + (n << 1) + c - '0', c = getchar();
return neg ? -n : n;
}
void wr(int n) {
static char o[11];
if(n < 0) putchar('-'), n = -n;
int i = 0; do o[i++] = n % 10 + '0'; while(n /= 10);
while(i--) putchar(o[i]);
}
int main() {
int l = 1, r = rd();
while(l <= r) {
int m = (l + r) >> 1;
printf("? %d\n", m);
fflush(stdout);
int x = rd();
if(!x) {
printf("= %d\n", m);
fflush(stdout);
break;
}
if(x < 0) r = m - 1;
else l = m + 1;
}
return 0;
}
