#include    <iostream>
#include    <cstring>

using namespace std;

int main()
{
    char s1[100] = "ac";
    char s2[500] = "ana are un ac. acum merg acasa! dar inainte voi merge la magazin de unde o sa-mi iau un_ac_si un acordeon.";
    char s3[500]; strcpy(s3, s2);

    char *p = strstr(s2, s1);
    while(p != NULL)
    {
        //cout << p << "\n";

        int c = p - s2;
        if(!(p[2] >= 'a' && p[2] <= 'z'))
        {
            strcpy(s3+c, s3+c+strlen(s1));
        }

        c += strlen(s1);
        p = strstr(s2 + c, s1);
    }
    cout << s3;
    return 0;
}