#include <bits/stdc++.h>
using namespace std;
void input(long long int n, long long int a[]) {
  for (long long int i = 0; i < n; ++i) cin >> a[i];
}
long long int bin_expo(long long int A, long long int B, long long int M) {
  long long int result = 1ll;
  while (B > 0) {
    if (B % 2 == 1) {
      result = (result * A) % M;
    }
    A = (A * A) % M;
    B = B / 2;
  }
  return result;
}
long long int gcd(long long int a, long long int b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long int lcm(long long int a, long long int b) {
  return (a * b) / gcd(a, b);
}
long long int n, l;
long long int a[101], b[101];
long long int dp[4001][200][3];
long long int solve(long long int left, long long int prev,
                    long long int flag) {
  if (left < 0) return 0LL;
  if (left == 0) return 1LL;
  if (dp[left][prev][flag] != -1) return dp[left][prev][flag];
  long long int res = 0;
  if (prev == -1) {
    for (long long int i = 0; i < n; ++i) {
      res += solve(left - a[i], i, 2);
      if (a[i] != b[i]) res += solve(left - b[i], i, 1);
      res %= 1000000007;
    }
  } else {
    for (long long int i = 0; i < n; ++i) {
      if (i != prev) {
        long long int cur;
        if (flag == 1) cur = a[prev];
        if (flag == 2) cur = b[prev];
        if (a[i] == cur)
          res += solve(left - a[i], i, 2);
        else if (b[i] == cur)
          res += solve(left - b[i], i, 1);
        res %= 1000000007;
      }
    }
  }
  return dp[left][prev][flag] = res % 1000000007;
}
int main() {
  memset(dp, -1, sizeof(dp));
  cin >> n >> l;
  for (long long int i = 0; i < n; ++i) cin >> a[i] >> b[i];
  cout << solve(l, -1, 0) << endl;
  return 0;
}
