<div class="box">
<div class="one">1. kutu</div>
<div class="two">2 kutu</div>
<div class="three">3. kutu</div>
<div class="four">4 kutu</div>
</div>

.box{
display:flex;
flex-wrap:wrap;
}
.box > div:not(.four){
flex:1;
}
.four{
width:100%;
}