// デバッグ #include using namespace std; using ll = long long; #define TYPE_OF( VAR ) remove_const::type >::type #define UNTIE ios_base::sync_with_stdio( false ); cin.tie( nullptr ) #define CEXPR( LL , BOUND , VALUE ) constexpr const LL BOUND = VALUE #define CIN( LL , A ) LL A; cin >> A #define ASSERT( A , MIN , MAX ) assert( MIN <= A && A <= MAX ) #define CIN_ASSERT( A , MIN , MAX ) CIN( TYPE_OF( MAX ) , A ); ASSERT( A , MIN , MAX ) #define FOR( VAR , INITIAL , FINAL_PLUS_ONE ) for( TYPE_OF( FINAL_PLUS_ONE ) VAR = INITIAL ; VAR < FINAL_PLUS_ONE ; VAR ++ ) #define QUIT return 0 #define RETURN( ANSWER ) cout << ( ANSWER ) << "\n"; QUIT #define CHECK_REDUNDANT_INPUT string VARIABLE_FOR_CHECK_REDUNDANT_INPUT = ""; cin >> VARIABLE_FOR_CHECK_REDUNDANT_INPUT; assert( VARIABLE_FOR_CHECK_REDUNDANT_INPUT == "" ); assert( ! cin ); // #define CHECK_REDUNDANT_INPUT string VARIABLE_FOR_CHECK_REDUNDANT_INPUT = ""; getline( cin , VARIABLE_FOR_CHECK_REDUNDANT_INPUT ); assert( VARIABLE_FOR_CHECK_REDUNDANT_INPUT == "" ); assert( ! cin ); int main() { CEXPR( ll , bound_N , 100000000 ); CIN_ASSERT( N , 1 , bound_N ); CHECK_REDUNDANT_INPUT; // (pa+b)/(p^2-1) > 1/N // <=> N(pa+b) > p^2-1 // <=> p^2 - Nap - (Nb+1) < 0 // <=> Na/2 - (sqrt((Na)^2+4(Nb+1)))/2 < p < Na/2 + (sqrt((Na)^2+4(Nb+1)))/2 ll answer = 0; ll Na = -N; CEXPR( ll , bound_ab , 10 ); CEXPR( ll , bound_p , 1000000000 ); FOR( a , 0 , bound_ab ){ Na += N; ll Na2 = Na * Na; double Na_half = Na / 2.0; ll Nb_plus = -N + 1; FOR( b , 0 , bound_ab ){ Nb_plus += N; double r = sqrt( Na2 + 4 * Nb_plus ) / 2.0; ll low = Na_half - r; if( low * low - Na * low - Nb_plus >= 0 ){ low++; } low = max( max( max( a , b ) + 1 , (ll)2 ) , low ); ll upp = Na_half + r; if( upp * upp - Na * upp - Nb_plus >= 0 ){ upp--; } upp = min( bound_p , upp ); if( low <= upp ){ answer += upp - low + 1; // デバッグ用 for( ll p = low ; p <= upp ; p++ ){ cout << "(p,a,b) = (" << p << "," << a << "," << b << ")" << endl; assert( ( p * a + b ) * N > p * p - 1 ); assert( 2 <= p && a <= p - 1 && b <= p - 1 && p <= bound_p ); } } } } RETURN( answer ); }