#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
using ll = long long;
using P = pair<int, int>;

int main(){
    long double x,y,r; cin>>x>>y>>r;
    r += 1e-14;
    int lx = ceil(x-r);
    int rx = floor(x+r);
    ll ans = 0;
    for(int i=lx; i<=rx; i++){
        double uy = floor(y + sqrt(r*r - (x-i)*(x-i)));
        double dy = ceil(y - sqrt(r*r - (x-i)*(x-i)));
        ans += uy - dy + 1;
    }
    cout << ans << endl;
    return 0;
}
#include<bits/stdc++.h> 
using namespace std;
namespace Sakurajima_Mai{
	#define ms(a) memset(a,0,sizeof(a))
	#define repi(i,a,b) for(int i=a,bbb=b;i<=bbb;++i)//attention reg int or reg ll ?
	#define repd(i,a,b) for(int i=a,bbb=b;i>=bbb;--i)
	#define reps(s) for(int i=head[s],v=e[i].to;i;i=e[i].nxt,v=e[i].to)
	#define ce(i,r) i==r?'\n':' '
	#define pb push_back 
	#define all(x) x.begin(),x.end()
	#define gmn(a,b) a=min(a,b)
	#define gmx(a,b) a=max(a,b)
	#define fi first
	#define se second   					  
	typedef long long ll;
	typedef unsigned long long ull;
	typedef double db;
	const int infi=2e9;//infi??,????inf????int
	const ll infl=4e18;
	inline ll ceil_div(ll a,ll b){ return (a+b-1)/b; }
	//std::mt19937 rnd(time(0));//std::mt19937_64 rnd(time(0));
}
using namespace Sakurajima_Mai;
namespace Fast_Read{
	inline int qi(){
	    int f=0,fu=1; char c=getchar();
	    while(c<'0'||c>'9'){ if(c=='-')fu=-1; c=getchar(); }
	    while(c>='0'&&c<='9'){ f=(f<<3)+(f<<1)+c-48; c=getchar(); }
	    return f*fu;
	}
	inline ll ql(){
		ll f=0;int fu=1; char c=getchar();
	    while(c<'0'||c>'9'){ if(c=='-')fu=-1; c=getchar(); }
	    while(c>='0'&&c<='9'){ f=(f<<3)+(f<<1)+c-48; c=getchar(); }
	    return f*fu;
	}
	inline db qd(){
	    char c=getchar();int flag=1;double ans=0;
	    while((!(c>='0'&&c<='9'))&&c!='-') c=getchar();
	    if(c=='-') flag=-1,c=getchar();
	    while(c>='0'&&c<='9') ans=ans*10+(c^48),c=getchar();
	    if(c=='.'){c=getchar();for(int Bit=10;c>='0'&&c<='9';Bit=(Bit<<3)+(Bit<<1)) ans+=(double)(c^48)*1.0/Bit,c=getchar();}
	    return ans*flag;
	}
}
namespace Read{
	#define si(a) scanf("%d",&a)
	#define sl(a) scanf("%lld",&a)
	#define sd(a) scanf("%lf",&a)
	#define ss(a) scanf("%s",a)
	#define rai(x,a,b) repi(i,a,b) x[i]=qi()
	#define ral(x,a,b) repi(i,a,b) x[i]=ql()
}
namespace Out{
	#define pi(x) printf("%d",x)
	#define pl(x) printf("%lld",x)
	#define ps(x) printf("%s",x)
	#define pc(x) printf("%c",x)
	#define pe() puts("")
}
namespace DeBug{
	#define MARK false
	#define DB if(MARK) 
	#define pr(x) cout<<#x<<": "<<x<<endl
	#define pra(x,a,b) cout<<#x<<": "<<endl; \
			repi(i,a,b) cout<<x[i]<<" ";	 \
			puts("");   
	#define FR(a) freopen(a,"r",stdin)
	#define FO(a) freopen(a,"w",stdout)
}
using namespace Fast_Read;
using namespace Read;
using namespace Out;
using namespace DeBug;
typedef long double ldb;
int main()
{
	ldb x,y,r; cin>>x>>y>>r;
	r+=1e-14;
	ll ans=0;
	repi(i,ceil(y-r),floor(y+r)){
		ldb dy=abs(y-i);
		if(dy>r) continue; 
		ldb dx=sqrt(r*r-dy*dy);
		ll lx=1ll*ceil(x-dx),rx=1ll*floor(x+dx);
		ans+=(rx-lx+1);
	}
	pl(ans),pe();
	return 0;
}
	