C I/O

#include <stdio.h>

int const MAX_LEN = 1024 * 1024;

int main() {
    FILE *fin = fopen("input.txt", "r");
    FILE *fout = fopen("output.txt", "w");

    char str[MAX_LEN];
    fgets(str, MAX_LEN, fin);

    char ch = fgetc(fin);

    fputc(ch, fout);
    fputs(str, fout);

    fclose(fin);
    fclose(fout);

    return 0;
}