s=a+aa+aaa+aaaa+aa...aaaa

main(){

int a,n,count=1;

long int sn=0,tn=0;

cout<<"input a and n:";

cin>>a>>n;

while(count<=n){

tn=tn+a;

sn=sn+tn;

a=a*10;

++count;}

cout<<"a+aa+aaa+a........"<<sn;