#include <stdio.h>

#define MAX 50

int main(){
	FILE *fp=NULL;
	FILE *fpout=NULL;
	char op, c;
	char ime1[MAX], ime2[MAX];
	
	scanf("%s %s %c", ime1, ime2, &op);
	fp = fopen(ime1, "r");
	fpout = fopen(ime2, "w");
	if(fp == NULL || fpout==NULL){
		printf("-1\n");
		return 1;
	}

	while((c=fgetc(fp))!=EOF){
		if(op=='u')
			c=toupper(c);
		else if(op=='l')
			c=tolower(c);
		fputc(c, fpout);
	}

	fclose(fp);
	fclose(fpout);
	return 0;
}