#include <bits/stdc++.h>
#define int long long
int mod = 1e9 + 7;
int add(int x, int y) {
x += y;
x %= mod;
return x;
}
signed main() {
int n;
std::cin >> n;
std::vector<int> d(n + 1), x(n + 1);
for(int i = 1; i <= n; i++) {
std::cin >> d[i] >> x[i];
}
std::vector<int> dp(n + 1, 0);
dp[1] = 1;
for(int i = 1; i <= n; i++) {
if(d[i] == 0) {
continue;
}
for(int t = 1; t <= x[i] && i + t * d[i] <= n; t++) {
dp[i + t * d[i]] = add(dp[i + t * d[i]], dp[i]);
}
}
int ans = 0;
for(int i = 1; i <= n; i++) {
ans = add(ans, dp[i]);
}
std::cout << ans;
}
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