#include <bits/stdc++.h>
#define x first
#define y second
#define int long long
using namespace std;
typedef pair<int,int> PII;
const int N = 1e6+10,mod = 998244353,INF=1e12;
const double eps = 1e-6;
void solve()
{
    int w,n,m;
    cin>>w>>n>>m;
    int cnt=0;
    while(cnt<m)
    {
        int x,y;
        cin>>x>>y;
        n+=x,m+=y;
        cnt++;
    }
    cout<<(n+w-1)/w<<"\n";
}

signed main()
{
    int T=1;
    cin.tie(0)->sync_with_stdio(false);
    //cin>>T;
    while(T--)
    {
        solve();
    }
    return 0;
}
/*
1
10 0

7
5 2
7 0
2 0

5
2 3
2 2
1 0
1 0
6 0
4 2
3 0
2 0
 */