2017-yo-t2.cpp

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

#define int long long

#define PB push_back
#define PPB pop_back
#define MK make_pair
#define ALL(V) V.begin(), V.end()
typedef pair<int, int> pii;
typedef pair<double, double> pdd;
typedef pair<string, int> psi;
typedef pair<int, pii> pipii;

constexpr int INF = 1LL << 61;
//constexpr int MOD = 1000000007;
//constexpr int MAX_N = 55;

int n, m;
vector<int> hoge;

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    cin >> n >> m;

    for (int i = 0; i < m; ++i) {
        int a, b;
        cin >> a >> b;
        if (n <= a) continue;
        hoge.PB(n - a);
    }

    sort(ALL(hoge));
    int ans = 0;
    for (int i = 0; i < hoge.size() - 1; ++i) ans += hoge[i];

    cout << ans << endl;
}