51nod1079
1 #include<cstdio>
2 #include<iostream>
3 using namespace std;
4 typedef unsigned long long ULL;
5 int p[11],r[11];
6
7 ULL Find(ULL x, int y)
8 {
9 ULL ret;
10 for(int i = 1; i < y; ++i)
11 {
12 if((ret = i*x) % y == 1) {
13 break;
14 }
15 }
16 return ret;
17 }
18
19 int main()
20 {
21 int n;
22 ULL Mul = 1;
23 cin>>n;
24 for(int i = 1; i <= n; ++i)
25 {
26 scanf("%d%d",&p[i],&r[i]);
27 Mul *= p[i];
28 }
29 ULL ans = 0;
30 for(int i = 1; i <= n; ++i)
31 {
32 ULL k = Find(Mul/p[i],p[i]);
33 for(int j = 1; j <= r[i]; ++j)
34 {
35 ans = (ans + k)%Mul;
36 }
37 }
38 printf("%llu\n",ans);
39 return 0;
40 }
