#include <stdio.h>
main(){
    char a[2000];
    int i, n;

    printf("Input letters.\n");
    gets( a );/* 改行まで文字列の入力 */

    n = 0 ;
    i = 0 ;
    while( a[i] != 0 ){
       if( a[i]=='r' ){     /* イコールは== */
          n = n + 1 ;
      }
      i = i + 1 ;
    }
    printf("number of letter 'r' in '%s' is %d\n",  a, n);
}