#include<bits/stdc++.h>

using namespace std;

const int maxn = 1e5+;

struct seg

{

    double l,r;

    bool operator < (const seg& x) const{

        return r < x.r || (r == x.r && l > x.l);

    }

}S[maxn];

int main()

{

    int L,D,N;

    while(~scanf("%d%d%d",&L,&D,&N)){

        double dis = D;

        for(int i = ; i < N; i++){

            double x,y; scanf("%lf%lf",&x,&y);

            double r = sqrt(dis*dis-y*y);

            S[i].l = x-r;

            S[i].r = x+r;

        }

        sort(S,S+N);

        double cur = -1e9;

        int ans = ;

        for(int i = ; i < N; i++){

            if(cur < S[i].l) {

                cur = S[i].r < L ?S[i].r : L;

                ans++;

            }

        }

        printf("%d\n",ans);

    }

    return ;

}