#include <algorithm>
#include <cmath>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rrep(i, n) for (int i = (n)-1; i >= 0; i--)
using namespace std;
using lli = long long int;
lli base1 = 123411237;
lli base2 = 565852344;
lli mod = 1e9 + 7;
lli powm(lli p, lli n)
{
    lli ans = 1;
    while (n) {
        if (n & 1) {
            ans = (ans * p) % mod;
        }
        p = (p * p) % mod;
        n /= 2;
    }
    return ans;
}
int main()
{
    lli n, q;
    cin >> n >> q;
    lli l, r, x;
    string s;
    lli h1 = 0, h2 = 0;
    map<lli, int> g1, g2;
    rep(i, q)
    {
        cin >> s;
        if (s == "!") {
            cin >> l >> r >> x;
            h1 = (h1 + x * (powm(base1, r) - powm(base1, l) + mod) % mod * powm(base1 - 1, mod - 2) + mod * mod) % mod;
            h2 = (h2 + x * (powm(base2, r) - powm(base2, l) + mod) % mod * powm(base2 - 1, mod - 2) + mod * mod) % mod;
            if (g1[h1] == 0 || g2[h2] == 0) {
                g1[h1] = i + 1;
                g2[h2] = i + 1;
            } else if (
                g1[h1] != 0 && g2[h2] != 0 && g1[h1] != g2[h2]) {
                g1[h1] = i + 1;
                g2[h2] = i + 1;
            }
        } else {
            //[l..r)にhash
            if (h1 == 0 && h2 == 0) {
                cout << 0 << endl;
            } else if (g1[h1] == 0 || g2[h2] == 0) {
                cout << i + 1 << endl;
            } else if (g1[h1] && g2[h2] && g1[h1] == g2[h2]) {
                cout << g1[h1] << endl;
            } else {
                cout << min(g1[h1], g2[h2]) << endl;
            }
        }
        //cout << i << ' ' << h1 << ' ' << h2 << endl;
    }
};