#include<>
int main(){
int i,max=0,count[130]={0};
char ch;
while(scanf("%c",&ch),ch!='\n'){
int c;
if(ch>='a'&&ch<='z'){
c=ch;
count[c]++;
}else if(ch>='A'&&ch<='Z'){ //大写字母则转化为对应的小写字母
c=ch+32;
count[c]++;
}
if(count[c]>max)
max=count[c];
}
for(i=60;i<129;i++){
if(count[i]==max){
printf("%c\n",i);
break;
}
}
return 0;
}