AC

for(i=1;i<=6;i++)
    {
        scanf("%s",word);
        if(!strcmp(word,"one")||!strcmp(word,"a")||!strcmp(word,"another")||!strcmp(word,"first"))
        {
            a[k]=1;
            k++;
        }
        else if(!strcmp(word,"two")||!strcmp(word,"both")||!strcmp(word,"second"))
        {
            a[k]=4;
            k++;
        }
        else if(!strcmp(word,"three")||!strcmp(word,"third"))
        {
            a[k]=9;
            k++;
        }
        else if(!strcmp(word,"four"))
        {
            a[k]=16;
            k++;
        }
        else if(!strcmp(word,"five"))
        {
            a[k]=25;
            k++;
        }
        else if(!strcmp(word,"six"))
        {
            a[k]=36;
            k++;
        }
        else if(!strcmp(word,"seven"))
        {
            a[k]=49;
            k++;
        }
        else if(!strcmp(word,"eight"))
        {
            a[k]=64;
            k++;
        }
        else if(!strcmp(word,"nine"))
        {
            a[k]=81;
            k++;
        }
        else if(!strcmp(word,"ten"))
        {
            a[k]=0;
            k++;
        }
        else if(!strcmp(word,"eleven"))
        {
            a[k]=21;
            k++;
        }
        else if(!strcmp(word,"twelve"))
        {
            a[k]=44;
            k++;
        }
        else if(!strcmp(word,"thirteen"))
        {
            a[k]=69;
            k++;
        }
        else if(!strcmp(word,"fourteen"))
        {
            a[k]=96;
            k++;
        }
        else if(!strcmp(word,"fifteen"))
        {
            a[k]=25;
            k++;
        }
        else if(!strcmp(word,"sixteen"))
        {
            a[k]=56;
            k++;
        }
        else if(!strcmp(word,"seventeen"))
        {
            a[k]=89;
            k++;
        }
        else if(!strcmp(word,"eighteen"))
        {
            a[k]=24;
            k++;
        }
        else if(!strcmp(word,"ninteen"))
        {
            a[k]=61;
            k++;
        }
        else if(!strcmp(word,"twenty"))
        {
            a[k]=0;
            k++;
        }
    }