#include <bits/stdc++.h>

using namespace std;

typedef long long i64;
typedef unsigned long long ui64;
typedef vector<i64> vi;
typedef vector<vi> vvi;
typedef pair<i64, i64> pi;

#define pb push_back
#define sz(a) i64((a).size())
#define all(c) (c).begin(), (c).end()
#define REP(s, e, i) for(i=(s); i < (e); ++i)
inline void RI(i64 &i) {scanf("%lld", &(i));}
inline void RVI(vi &v) { for(i64 i=0;i<sz(v);++i) { RI(v[i]); } }
inline void RVVI(vvi &vv) { for(i64 i=0;i<sz(vv);++i) { RVI(vv[i]); } }
inline void WI(const i64 &i) {printf("%lld\n", i);}
inline void WVI(const vi &v, char sep=' ') { for(i64 i=0;i<sz(v);++i) { if(i != 0){ printf("%c", sep); } printf("%lld", v[i]);} printf("\n"); }
inline void WS(const string &s) { printf("%s\n", s.c_str()); }
inline void WB(bool b, const string &yes, const string &no) { if(b){ WS(yes);} else { WS(no);} }
inline void YESNO(bool b) { WB(b, "YES", "NO"); }
inline void YesNo(bool b) { WB(b, "Yes", "No"); }
#define BUF_LENGTH 1000000
inline void RS(string &s) {static char buf[BUF_LENGTH]; scanf("%s", buf); s = buf;}
template<typename T> inline bool IN(T &S, const typename T::key_type &key) {
  return S.find(key) != S.end();
}
template<typename T> inline bool ON(const T &b, i64 idx) {
  return ((T(1) << idx) & b) != 0;
}

template<long long M, typename T=long long>
struct modint {
  modint(T v=T(0)) : val((v >= 0 ? v : (M - ((-v) % M))) % M) {}
  using this_type = modint<M, T>;
  T val;
  this_type operator++(int) {
    this_type ret = *this;
    val++; val %= M;
    return ret;
  }
  this_type operator--(int) {
    this_type ret = *this;
    val += M-1; val %= M;
    return ret;
  }
  this_type &operator++() {
    val++; val %= M;
    return *this;
  }
  this_type &operator--() {
    val += M-1; val %= M;
    return *this;
  }
  this_type operator+() const { return *this; }
  this_type operator-() const { return this_type(M-val); };
  friend this_type operator+(const this_type &lhs, const this_type &rhs) {
    return this_type(lhs) += rhs;
  }
  friend this_type operator-(const this_type &lhs, const this_type &rhs) {
    return this_type(lhs) -= rhs;
  }
  friend this_type operator*(const this_type &lhs, const this_type &rhs) {
    return this_type(lhs) *= rhs;
  }
  friend this_type operator/(const this_type &lhs, const this_type &rhs) {
    return this_type(lhs) /= rhs;
  }
  this_type pow(long long b) const {
    this_type ret = 1, a = *this;    
    while(b != 0) {
      if(b % 2 != 0) {
        ret *= a;
      }
      b /= 2;
      a = a * a;
    }
    return ret;
  }
  this_type inv() const {
    return pow(M-2);
  }
  this_type& operator+=(const this_type &rhs) {
    val += rhs.val; val %= M; return *this;
  }
  this_type& operator-=(const this_type &rhs) {
    val += M - rhs.val; val %= M; return *this;
  }
  this_type& operator*=(const this_type &rhs) {
    val *= rhs.val; val %= M; return *this;
  }
  this_type& operator/=(const this_type &rhs) {
    *this *= rhs.inv(); return *this;
  }
  friend bool operator==(const this_type &lhs, const this_type &rhs) {
    return lhs.val == rhs.val;
  }
  friend bool operator!=(const this_type &lhs, const this_type &rhs) {
    return lhs.val != rhs.val;
  }
  T mod() const {return M;}
};

using mi = modint<998244353>;
using vmi = vector<mi>;
using vvmi = vector<vmi>;

inline mi S0(mi v) {
  return v;
}

mi inv_2 = mi(2).inv();
mi inv_6 = mi(6).inv();
inline mi S1(mi v) {
  return v * (v + 1) * inv_2;
}

inline mi S2(mi v) {
  return v * (v + 1) * (2 * v + 1) * inv_6;
}

inline mi S3(mi v) {
  mi s = S1(v);
  return s * s;
}

inline mi F(mi v, mi L) {
  return (- S3(v) + (L - 3) * S2(v) + (3 * L - 2) * S1(v) + 2 * L * S0(v)) * inv_2;
}

inline mi G(mi l, mi r, mi L) {
  return F(r-1, L) - F(l-1, L);
}

int main(int argc, char *argv[]) {
  i64 i, j, k;
  i64 N; cin >> N;
  vi T(N), V(N);
  mi L = 0;
  REP(0, N, i) {
    RI(T[i]); RI(V[i]);
    L += T[i];
  }

  mi ans = 0;
  mi l = 0;
  REP(0, N, i) {    
    //cerr << G(l, l + T[i], V[i]).val << endl;
    ans += G(l, l + T[i], L) * mi(V[i]);
    l += T[i];
  }

  WI(ans.val);

  return 0;
}