#include 
    
     #define ll long long#define INF 2147483647#define mem_INF 2139062143#define ll_INF 9223372036854775807#define eps 1e-8#define fuckrand() ( ( rand() << 15 ) ^ rand() )using namespace std;inline int read() {    int x = 0,tmp = 1;char ch = getchar();    while( ch < '0' || ch > '9' ) {if ( ch == '-' ) tmp = -1; ch = getchar();}    while( ch >= '0' && ch <= '9'){x = x * 10 + ch - '0'; ch = getchar(); }    return x * tmp;}bool _map[51][51];int N, M, k1, k2, p[2600][2], ans = INF;bool dir_1( int x, int y ) {    return !( x + 1 > N || _map[x + 1][y] );}bool dir_2( int x, int y ) {    return !( y + 1 > M || _map[x][y + 1] );}bool dir_3( int x, int y ) {    return !( x - 1 < 1 || _map[x - 1][y] );}bool dir_4( int x, int y ) {    return !( y - 1 < 1 || _map[x][y - 1] );}inline void dfs_2( int x, int y, int now, int sum ) {    if( sum > ans ) return;    if( now >= ( N * M ) >> 1 ) {        sum = max( k1 * abs( x - p[now][0] ) + k2 * abs( y - p[now][1] ), sum );        ans = min( ans, sum );        return;    }    if( ( ( dir_2( x, y ) && dir_4( x, y ) ) && !( dir_1( x, y ) || dir_3( x, y ) ) ) ||         ( !( dir_2( x, y ) || dir_4( x, y ) ) && ( dir_1( x, y ) && dir_3( x, y ) ) )  ) return;     _map[x][y] = 1;    sum = max( k1 * abs( x - p[now][0] ) + k2 * abs( y - p[now][1] ), sum );    if( dir_1( x, y ) ) dfs_2( x + 1, y, now + 1, sum );    if( dir_2( x, y ) ) dfs_2( x, y + 1, now + 1, sum );    if( dir_3( x, y ) ) dfs_2( x - 1, y, now + 1, sum );    if( dir_4( x, y ) ) dfs_2( x, y - 1, now + 1, sum );    _map[x][y] = 0;}inline void dfs_1( int x, int y, int now ) {    if( now > ( M * N ) >> 1 ) {        dfs_2( x, y, 1, 0 );        return;    }    if( ( ( dir_2( x, y ) && dir_4( x, y ) ) && !( dir_1( x, y ) || dir_3( x, y ) ) ) ||         ( !( dir_2( x, y ) || dir_4( x, y ) ) && ( dir_1( x, y ) && dir_3( x, y ) ) )  ) return;     _map[x][y] = 1;    p[now][0] = x; p[now][1] = y;    if( dir_1( x, y ) ) dfs_1( x + 1, y, now + 1 );    if( dir_2( x, y ) ) dfs_1( x, y + 1, now + 1 );    if( dir_3( x, y ) ) dfs_1( x - 1, y, now + 1 );    if( dir_4( x, y ) ) dfs_1( x, y - 1, now + 1 );    _map[x][y] = 0;}int main() {    N = read(), M = read(), k1 = read(), k2 = read();    dfs_1( 1, M, 1 );    printf( "%d\n", ans );    return 0;}