const fs = require('fs');
const input = fs.readFileSync('/dev/stdin').toString().split(" ");
const A = Number(input[0]);
const B = Number(input[1]);
const C = Number(input[2]);
// B >= C 손익분기점 없음
if(B >= C) console.log(-1);
else {
let D = Math.abs((A/(B-C))-1);
console.log(D);
}
Y29uc3QgZnMgPSByZXF1aXJlKCdmcycpOwpjb25zdCBpbnB1dCA9IGZzLnJlYWRGaWxlU3luYygnL2Rldi9zdGRpbicpLnRvU3RyaW5nKCkuc3BsaXQoIiAiKTsKCmNvbnN0IEEgPSBOdW1iZXIoaW5wdXRbMF0pOwpjb25zdCBCID0gTnVtYmVyKGlucHV0WzFdKTsKY29uc3QgQyA9IE51bWJlcihpbnB1dFsyXSk7CgovLyBCID49IEMg7IaQ7J2167aE6riw7KCQIOyXhuydjAppZihCID49IEMpIGNvbnNvbGUubG9nKC0xKTsKZWxzZSB7CiAgICBsZXQgRCA9IE1hdGguYWJzKChBLyhCLUMpKS0xKTsKICAgIGNvbnNvbGUubG9nKEQpOwp9