include

include

using namespace std;

int main(){

char n;
char i;
int j[26]{};
int k[26]{};
cin>>i;
while(cin>>n){
    if(n==i){
        j[n-97]++;
        k[n-97]++;
    }
    i=n;
}
sort(j,j+26,[](int a,int b)->bool{return a>b;});

for(int m=0;m<26;m++){
    if(j[m]==j[m-1]&&m>0)continue;
    for(int x=0;x<26;x++){
        if(j[m]!=0&&k[x]==j[m]){
            cout<<char(x+97)<<char(x+97)<<' ';
        }
    }
}


return 0;

}