Submission #19636

#	Time	Username	Problem	Language	Result	Execution time	Memory
19636		yongwhan	Σ (kriii4_P2)	C++98	100 / 100	17 ms	1720 KiB

P2

#include<bits/stdc++.h>
using namespace std;

typedef long long ll;

const int mod=1e9+7;

ll exp(ll a, ll b, ll m) {
  ll r=1;
  while(b) {
    if(b%2) r=(r*a)%m;
    a=(a*a)%m;
    b/=2;
  }
  return r;
}

ll inv(ll a, ll m) {
  return exp(a,m-2,m);
}

int main() {
  int m; cin>>m;
  ll ret=0;
  for (int i=0; i<m; i++) {
    ll n,s; cin>>n>>s;
    ret=(ret+s*inv(n,mod))%mod;
  }
  cout << ret << endl;
  return 0;
}

• Subtask 1: 100 / 100