D.cpp

// #pragma GCC optimize("Ofast,unroll-loops")
// #pragma GCC target("avx,avx2,fma")

#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define ull unsigned long long
#define dd double
#define ld long double
#define sl(n) scanf("%lld", &n)
#define si(n) scanf("%d", &n)
#define sd(n) scanf("%lf", &n)
#define pll pair <ll, ll>
#define pii pair <int, int>
#define mp make_pair
#define pb push_back
#define all(v) v.begin(), v.end()
#define inf (1LL << 61)
#define loop(i, start, stop, inc) for(ll i = start; i <= stop; i += inc)
#define for1(i, stop) for(ll i = 1; i <= stop; ++i)
#define for0(i, stop) for(ll i = 0; i < stop; ++i)
#define rep1(i, start) for(ll i = start; i >= 1; --i)
#define rep0(i, start) for(ll i = (start-1); i >= 0; --i)
#define ms(n, i) memset(n, i, sizeof(n))
#define casep(n) printf("Case %lld:", ++n)
#define pn printf("\n")
#define pf printf
#define EL '\n'
#define fastio std::ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define eps 1e-9

inline ld sq(ld x) {return x*x;}

inline ld dist(ld x1, ld y1, ld x2, ld y2)
{
    return sq(x1-x2) + sq(y1-y2);
}

int main()
{
    ld x, y, r;
    cin >> x >> y >> r;

    ld r2 = r*r;

    ll start = x, ans = 0;

    for(ll xi = start+1; ; xi++) {

        if(dist(xi, y, x, y)-eps > r2)
            break;

        ll lo = y-1e11, hi = y, mn=1, mx=0;

        while(lo <= hi) {
            ll mid = lo+hi >> 1;

            if(dist(xi,mid, x, y)-eps > r2)
                lo = mid + 1;
            else {
                hi = mid - 1;
                mn = mid;
            }
        }

        lo = y, hi = y+1e11;

        while(lo <= hi) {
            ll mid = lo+hi >> 1;

            if(dist(xi, mid, x, y)-eps > r2)
                hi = mid-1;
            else {
                lo = mid + 1;
                mx = mid;
            }
        }

        ans += (mx-mn+1);
    }

    for(ll xi = start; ; xi--) {

        if(dist(xi, y, x, y)-eps > r2)
            break;

        ll lo = y-1e11, hi = y, mn=1, mx=0;

        while(lo <= hi) {
            ll mid = lo+hi >> 1;

            if(dist(xi,mid, x, y)-eps > r2)
                lo = mid + 1;
            else {
                hi = mid - 1;
                mn = mid;
            }
        }

        lo = y, hi = y+1e11;

        while(lo <= hi) {
            ll mid = lo+hi >> 1;

            if(dist(xi, mid, x, y)-eps > r2)
                hi = mid-1;
            else {
                lo = mid + 1;
                mx = mid;
            }
        }

        ans += (mx-mn+1);
    }

    cout << ans << EL;

    return 0;
}