#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char* argv[])
{
    char c;
    int len_new = 0;
    FILE *f1, *f2;
    int len3, i = 0, f = 0;
    long pos = 0;
    while (argv[3][i] != '\0')
    {
        ++i;
    }
    len3 = i;
    f1 = fopen(argv[1], "r");
    f2 = fopen(argv[2], "w");
    if ( (argc < 4) || (f1 == NULL) || (f2 == NULL) )
    {
        printf("Wrong input\n");
        exit(1);
    }
    while ( (c = fgetc(f1)) != EOF)
    {
        f = 0;
        if (c != argv[3][0])
        {
            fputc(c, f2);
        }
        if (c == argv[3][0])
        {
            pos=ftell(f1) - 1;
            fseek(f1, -1, SEEK_CUR);
            for (i = 0;i < len3; i++)
            {
                c = fgetc(f1);
                if (c != argv[3][i])
                {
                    f = 1;
                    break;
                }
            }
            if (f == 0)
            {
                for (int j = 0; j < strlen(argv[4]); j++)
                    fputc(argv[4][j], f2);
            }
            if (f == 1)
            {
                fseek(f1, -(i+1), SEEK_CUR);
                c = fgetc(f1);
                fputc(c, f2);
            }

        }
    }
    fclose(f1);
    fclose(f2);
    return(1);
}