// editor3
#include<stdio.h>
#include<string.h>
int main(){
    char str[101];
    scanf("%s", str);
    char *ptr = str;
    char min_char = *ptr;
    while(*ptr != '\0'){
        if (isdigit(*ptr)){
            return 0;
        }
        if(*ptr < min_char){
            min_char = *ptr;
        }
        ptr++;
    }
    printf("%c\n", min_char);
    return 0;
}