#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MAXN = 501;
const ll MOD = (ll)1e9 + 7;
ll A[MAXN],B[MAXN],N;
vector<ll> dp[MAXN],sum[MAXN];
inline ll get_sum(int idx,int i,int j){
i -= A[idx];
j -= A[idx];
i = max(i,0);
if(i > j) return 0;
if(i == 0) return sum[idx][j];
else return sum[idx][j] - sum[idx][i-1];
}
int main(){
cin >> N;
for(int i = 1;i<=N;i++){
cin >> A[i] >> B[i];
dp[i].assign(B[i] - A[i] + 1,0);
sum[i].assign(B[i] - A[i] + 1,0);
}
for(int j = A[N];j<=B[N];j++){
dp[N][j - A[N]] = 1;
sum[N][j - A[N]] = dp[N][j - A[N]];
if(j - A[N] != 0) sum[N][j - A[N]] += sum[N][j - A[N] - 1];
}
for(int i = N-1;i>=1;i--){
for(int j = A[i];j<=B[i];j++){
dp[i][j - A[i]] = 1;
for(ll k = i+1;k<=N;k++){
dp[i][j - A[i]] = (dp[i][j - A[i]] + get_sum(k,j+1,B[k]));
}
dp[i][j - A[i]] %= MOD;
}
for(int j = A[i];j<=B[i];j++){
sum[i][j - A[i]] = dp[i][j - A[i]];
if(j - A[i] != 0) sum[i][j - A[i]] += sum[i][j - A[i] - 1];
sum[i][j - A[i]] %= MOD;
}
}
ll tot = 0;
for(int i = 1;i<=N;i++) tot = (tot + sum[i].back()) % MOD;
if(tot < 0) tot += MOD;
cout << tot << endl;
return 0;
}
