B.cpp - Round 434

#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define mk make_pair
#define fi first
#define se second
#define fastcin ios_base::sync_with_stdio(false)

typedef long long ll;
const int INF = 0x3f3f3f3f;
const double PI = acos(-1.0);

int k[107], f[107];

int main (void) {
    fastcin;
    int n, m;
    cin >> n >> m;
    int tmp;
    for(int i=0;i<m;i++){
        cin >> k[i];
        k[i]--;
        cin >> f[i];
        f[i]--;
    }
    //v[i] = lugar que está i
    int cnt = 0;
    int answ;
    for(int val = 1; val < 101; val++){
        bool flag = true;
        for(int i = 0;i < m; i++){
            if(k[i] / val != f[i] && k[i] != 0){
                flag = false;
                break;
            }
        }
        if(flag == true){
            cnt++;
        }

        if(cnt == 1 && flag == true){
            answ = n / val;
        }
    }
    if(cnt != 1)
        cout << -1 << endl;
    else
        cout << answ+1 << endl;


    return 0;
}