var fs = require('fs');
var input = fs.readFileSync('example.txt', 'utf8').toString().trim().split('\n');
input = parseInt(input);
function factorial (param1){
if(param1== 2 || param1 == 1){
return 1
}else if(param1==0){
return 0;
}else if(param1>2){
return factorial(param1-1) + factorial(param1-2);
}
}
console.log(factorial(input));