%{
#include <stdio.h>
extern FILE *yyin, *yyout;  // External file pointers for input and output
%}
 
%% 
. { fprintf(yyout, "%s", yytext); }  // Print each matched character to output file
%% 
 
int main() {
    extern FILE *yyin, *yyout;
 
    // Open input.txt for reading and output.txt for writing
    yyin = fopen("input.txt", "r");
    if (!yyin) {
        perror("Error opening input file");
        return 1;
    }
 
    yyout = fopen("output.txt", "w");
    if (!yyout) {
        perror("Error opening output file");
        return 1;
    }
 
    yylex();  // Start lexical analysis
    fclose(yyin);  // Close input file after processing
    fclose(yyout); // Close output file after processing
 
    return 0;
}
 

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VGhpcyBpcyBOIFIgWWFkYXY=

This is N R Yadav