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#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <vector>
#include <set>
#include <map>
#include <cmath>
#include <list>
#include <ctime>
#include <sstream>
#include <queue>
#include <stack>
#include <bitset>
#include <unordered_set>
#include <unordered_map>
using namespace std;
typedef vector<int> vi;
typedef pair<int,int> pii;
typedef long long ll;
typedef short int sint;
#define FOR(x, b, e) for(int x=(b); x<=(e); ++x)
#define FORD(x, b, e) for(int x=((int)(b))-1; x>=(e); --x)
#define REP(x, n) for(int x=0; x<(n); ++x)
#define ALL(c) c.begin(),c.end()
#define SIZE(x) ((int)((x).size()))
#define PB push_back
#define ST first
#define ND second
#define mp(x,y) make_pair(x,y)
#define DEBUG 1
#define debug(x) {if (DEBUG)cerr <<#x <<" = " <<x <<endl; }
#define debugv(x) {if (DEBUG) {cerr <<#x <<" = "; FOREACH(it, (x)) cerr <<*it <<", "; cout <<endl; }}
#define REMAX(a,b) (a)=max((a),(b));
#define REMIN(a,b) (a)=min((a),(b));
#define wez(n) int (n); scanf("%d",&(n));
#define wez2(n,m) int (n),(m); scanf("%d %d",&(n),&(m));

const int DL = 1000000 * 6;
const int MOD = 1000000000 + 7;
int n;
string tekst;
vector<vector<int>> wynik;
set<int> wys;
map<int, int> mapowanie;

void split(const std::string &s, char delim, std::vector<std::string> &elems) {
    std::stringstream ss;
    ss.str(s);
    std::string item;
    while (std::getline(ss, item, delim)) {
        elems.push_back(item);
    }
}

// trim from start (in place)
static inline void ltrim(std::string &s) {
    s.erase(s.begin(), std::find_if(s.begin(), s.end(),
            std::not1(std::ptr_fun<int, int>(std::isspace))));
}

// trim from end (in place)
static inline void rtrim(std::string &s) {
    s.erase(std::find_if(s.rbegin(), s.rend(),
            std::not1(std::ptr_fun<int, int>(std::isspace))).base(), s.end());
}

// trim from both ends (in place)
static inline void trim(std::string &s) {
    ltrim(s);
    rtrim(s);
}

// trim from start (copying)
static inline std::string ltrimmed(std::string s) {
    ltrim(s);
    return s;
}

// trim from end (copying)
static inline std::string rtrimmed(std::string s) {
    rtrim(s);
    return s;
}

// trim from both ends (copying)
static inline std::string trimmed(std::string s) {
    trim(s);
    return s;
}

int parsuj(string d) {
	int mn = 1;
	int pocz = 0;
	if (d[pocz] == '~') {
		mn = -1;
		pocz = 2;
	} else {
		pocz = 1;
	}
	return mn * atoi(d.substr(pocz).c_str());
}

bool getBit(int maska, int pos) {
	return (maska & (1 << pos)) > 0;
}

bool ok(int maska) {
	REP(i, SIZE(wynik)) {
		bool ok = false;
		for (auto elem : wynik[i]) {
			int curr = elem;
			int bit = getBit(maska, mapowanie[abs(curr)]);
			// printf("elem: %d, bit: %d\n", elem, bit);
			if (curr > 0 && bit) {
				ok = true;
				break;
			}
			if (curr < 0 && !bit) {
				ok = true;
				break;
			}
		}
		if (!ok) {
			return false;
		}
	}
	return true;
}

int main() {
	cin >> n;
	getline(cin, tekst);
	getline(cin, tekst);
	vector<string> words;
	split(tekst, '^', words);
	vector<string> pom;
	for (auto word : words) {
		string tri = trimmed(word);
		pom.PB(tri.substr(1, SIZE(tri) - 2));
	}
	words = pom;
	vector<vector<string>> slowa;
	for (auto word : words) {
		vector<string> podslowa;
		split(word, 'v', podslowa);
		vector<string> pom;
		for (auto slowo : podslowa) {
			pom.PB(trimmed(slowo));
		}
		podslowa = pom;
		slowa.PB(podslowa);
	}
	for (auto c : slowa) {
		vector<int> cur;
		// printf("c: ");
		for (auto d : c) {
			cur.PB(parsuj(d));
			wys.insert(abs(cur.back()));
			// printf("%d ", cur.back());
		}
		// printf("\n");
		wynik.PB(cur);
	}
	int ind = 0;
	for (auto wystek : wys) {
		mapowanie[wystek] = ind++;
	}

	int res = 0;
	REP(i, 1 << SIZE(wys)) {
		// printf("dla maski: %d - ", i);
		if (ok(i)) {
			++res;
			if (res == MOD) {
				res = 0;
			}
			// printf("ok!\n");
		} else {
			// printf("nie ok\n");
		}
	}
	REP(i, n - SIZE(wys)) {
		res = (res * 2) % MOD;
	}
	printf("%d\n", res);
	return 0;
}