#include<stdio.h>
int main(){
int hash[128]={0};
char data[1000]={0};
while(scanf("%s", data) != EOF){
int lenth;
for(lenth=0; data[lenth] != '\0'; lenth++){
hash[data[lenth]]++;
}
int mmax = 0;
int loc = 0;
lenth =0;
for(int x=48; x<128; x++){
if(hash[x] != 0)lenth++;
}
for(int i=0; i<lenth; i++){
for(int x=48; x<128; x++){
if(hash[x]>mmax){
loc = x;
mmax = hash[x];
}
}
printf("%c", loc);
hash[loc] = 0;
mmax = 0;
}
printf("\n");
}
}