/**
 *    Author: Nachiket Kanore
 *    Created: Monday 18 April 2022 10:14:21 PM IST
 **/
#include <bits/stdc++.h>

#define int int64_t
#define sz(x) (int)(x.size())
#define ALL(x) (x).begin(), (x).end()
#define F0R(i, R) for (int i = (0); i < (R); ++i)
#define FOR(i, L, R) for (int i = (L); i <= (R); ++i)

using namespace std;
const int MOD = 1e9 + 7;
const int SZ  = 105;

int add(int a, int b) {
    int res = a + b;
    if (res >= MOD)
        return res % MOD;
    return res;
}

int mult(int a, int b) {
    long long res = a;
    res *= b;
    if (res >= MOD)
        return res % MOD;
    return res;
}

struct matrix {
    int arr[SZ][SZ];

    void reset() {
        memset(arr, 0, sizeof(arr));
    }

    void makeiden() {
        reset();
        for (int i = 0; i < SZ; i++) {
            arr[i][i] = 1;
        }
    }

    matrix operator+(const matrix& o) const {
        matrix res;
        for (int i = 0; i < SZ; i++) {
            for (int j = 0; j < SZ; j++) {
                res.arr[i][j] = add(arr[i][j], o.arr[i][j]);
            }
        }
        return res;
    }

    matrix operator*(const matrix& o) const {
        matrix res;
        for (int i = 0; i < SZ; i++) {
            for (int j = 0; j < SZ; j++) {
                res.arr[i][j] = 0;
                for (int k = 0; k < SZ; k++) {
                    res.arr[i][j] = add(res.arr[i][j], mult(arr[i][k], o.arr[k][j]));
                }
            }
        }
        return res;
    }
};

matrix power(matrix a, int b) {
    matrix res;
    res.makeiden();
    while (b) {
        if (b & 1) {
            res = res * a;
        }
        a = a * a;
        b >>= 1;
    }
    return res;
}
int N, M, K, H;

int32_t main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cin >> N >> M >> K >> H;
    if (K == 0) {
        cout << "0\n";
        return 0;
    }
    matrix A;
    A.reset();
    F0R(i, M) {
        int u, v;
        cin >> u >> v;
        A.arr[u][v] = 1;
        A.arr[v][u] = 1;
    }
    A       = power(A, K);
    int ans = A.arr[H][H] % MOD;
    cout << ans;
    return 0;
}