(async () => {
    let input = '';
    for await (const chunk of process.stdin) input += chunk;
    
    const [a, b, c, d] = input.split(/\s/).map(v => +v);
    if(b <= 0 && d <= 0){
        console.log(a * c);
    }else if(b <= 0){
        console.log(b * c);
    }else if(d <= 0){
        console.log(a * d);
    }else{
        console.log(b * d);
    }
})();
