#include <cstdio>
#include <cstdlib>
#include <algorithm>

#define X first
#define Y second

const int N = 1005;

using namespace std;
pair< int, int > tmp, L, A[ N ], B[ N ];
int n, dead[ N ] = { 0 };

int pronadji( void ) {
	int ind = -1; double nbvis = -1;
	
	for( int i = 0; i < n; ++i ) {
		if( dead[ i ]  ||  L.X < A[ i ].X  ||  L.X > B[ i ].X ) continue;
		double nagib = ( B[ i ].Y - A[ i ].Y ) / ( double )( B[ i ].X - A[ i ].X );
		double vis = A[ i ].X + ( L.X - A[ i ].X ) * nagib;
		if( vis < ( double )L.Y  &&  vis > nbvis ) { nbvis = vis; ind = i; }
	}
	
	dead[ ind ] = 1;
	return( ind );
}

int main( void ) {
	scanf( "%d %d %d", &L.X, &L.Y, &n );
	for( int i = 0; i < n; ++i ) {
		scanf( "%d %d %d %d", &A[ i ].X, &A[ i ].Y, &B[ i ].X, &B[ i ].Y );
		if( A[ i ].X > B[ i ].X ) { tmp = A[ i ]; A[ i ] = B[ i ]; B[ i ] = tmp; }
	}
	
	int sudar = 0;
	while( 1 ) {
		int ind = pronadji();
		if( ind == -1 ) break;
		
		++sudar;
		L = ( A[ ind ].Y < B[ ind ].Y  ?  A[ ind ] : B[ ind ] );
	}
	
	printf( "%d\n", L.X );
	//printf( "(%d)\n", sudar );
	return( 0 );
}