>>120 便乗
#include <stdio.h>
#include <string.h>

int main(void)
{
    char buf[1024], rep[2048], word1[32], word2[32], *p = buf, *q = rep;
    scanf("%[^\n]%s%s", buf, word1, word2);
    while(*p){
        if(!strncmp(p, word1, strlen(word1))) strcpy(q, word2), p += strlen(word1), q += strlen(word2);
        else *q++ = *p++;
    }
    *q = '\0';
    puts(rep);
    return 0;
}