Блок-схемы

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#include <iostream>
#include <cmath>
using namespace std;
using ll  = long long;
ll a,b;

ll S(ll x){
    return (2*3 + 3 * (x - 1)) * x / 2;
}



bool f(ll N){
    ll c1 = 0;
    bool can = 1;
    if (N == 0){
        c1 = 0;
    }
    else{
        while (true){
            if (S(c1) == N){
                break;
            }
            if (S(c1) > N){
                can = 0;
                break;
            }
            c1++;
        }
    }
    if (can){
        ll c2 = 0;
        if (c1 == 0){
            c2 = 0;
        }
        else{
            while (true){
                if (S(c2) == c1){
                    break;
                }
                if (S(c2) > c1){
                    can = 0;
                    break;
                }
                c2++;
            }
        }
        if (can){
            return c2 == 18;
        }
        else return false;
    }
    else return false;
}


int main()
{
    int x = 0;
    ll ans = -666;
    while (true){
        //cout<<x<<'\n';
        if (x > 4e6) {
            cout<<x<<'\n';
            break;
        }
        if (f(x)) {
            cout<<"x = "<<x<<'\n';
            break;
        }
        x++;
    }
}
//Программа может вообще не дойти -- тогда return false