#include <bits/stdc++.h>

using namespace std;

bool cmp(pair<int, int> x, pair<int, int> y) { return y.first * x.second < x.first * y.second; }
const int MAXN = 1e5;
pair<int, int> f[MAXN];
int a[MAXN], b[MAXN];

int main() {
    // ios::sync_with_stdio(false);
    // cin.tie(0);
    int n, i, j;
    long long UPD = 0;
    // cin >> n;
    scanf("%d", &n);
    for (i = 0; i < n; ++i) {
        // cin >> a[i] >> b[i];
        scanf("%d%d", a + i, b + i);
        // scanf("%d", b + i);
    }
    for (i = 0; i < n; ++i) {
        f[i] = pair<int, int>(a[i], b[i]);
    }

    sort(f, f + n, cmp);
    long long time = 0;
    for (i = 0; i < n; ++i) {
        time += f[i].second;
        UPD += time * f[i].fist;
        // for (j = 0; j <= i; ++j) UPD += f[i].first * f[j].second;
    }
    // cout << UPD;
    printf("%lld", UPD);
    return 0;
}

/sandbox/1/a.cpp: In function 'int main()':
/sandbox/1/a.cpp:30:24: error: 'struct std::pair<int, int>' has no member named 'fist'; did you mean 'first'?
         UPD+=time*f[i].fist;
                        ^~~~
                        first
/sandbox/1/a.cpp:16:11: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
      scanf("%d", &n);
      ~~~~~^~~~~~~~~~
/sandbox/1/a.cpp:19:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d%d", a + i, b + i);
         ~~~~~^~~~~~~~~~~~~~~~~~~~~~