#define _CRT_SECURE_NO_WARNINGS

#include <string.h>
#include <stdio.h>
#include <stdlib.h>

void addChar(char** res, char s) {
    int size = strlen((*res));
    (*res) = (char*)realloc((*res), (size + 2) * sizeof(char));
    (*res)[size + 1] = '\0';
    (*res)[size] = s;
}

char* getResult(char* s) {
    int i = 0;
    int j = strlen(s) - 1;
    int isNotDup = 0;
    char temp;
    char* res = (char*)malloc(sizeof(char));
    res[0] = '\0';
    for (i = 0; i <= j; i++) {
        isNotDup = 1;
        if (s[i] == s[i + 1]) {
            temp = s[i];
            i++;
            while (s[i + 1] == temp)
                i++;
            addChar(&res, '_');
            for (; (j != i && isNotDup); j--) {
                if (s[j] == s[j - 1]) {
                    isNotDup = 0;
                    temp = s[j];
                    j--;
                    while (s[j - 1] == temp)
                        j--;
                    addChar(&res, '_');
                }
                else {
                    addChar(&res, s[j]);
                }
            }
        }
        else {
            addChar(&res, s[i]);
        }
    }
    return res;
}



int main() {
    char s1[100];
    char* res;
    printf("Enter string: ");
    fgets(s1, sizeof(s1), stdin);
    s1[strlen(s1) - 1] = '\0';
    res = getResult(s1);
    printf("\nResult string: %s", res);
    return 0;
}