#include<bits/stdc++.h>
#define int long long
#define double long double
#define con continue
using namespace std;
double jia,z,yi,c,ans;
signed main()
{
	cin>>jia>>z>>c;
	yi=jia-2*z;
	cout<<(long long)yi/c+1;
	return 0;
}

这段代码能AC，可是……没有用ceil函数